Andusomeran (CX-038839 Omicron XBB.1.5): A Comprehensive Report on the Monovalent COVID-19 mRNA Vaccine

1. Executive Summary

CX-038839 Omicron (XBB.1.5), generically known as Andusomeran and marketed under brand names such as Spikevax XBB.1.5, is a monovalent messenger RNA (mRNA) vaccine developed by Moderna. It is designed to elicit a protective immune response against the XBB.1.5 subvariant of the SARS-CoV-2 Omicron lineage, which was a predominant circulating strain during its development period.[1] The vaccine employs nucleoside-modified mRNA technology, encoding the prefusion-stabilized spike (S) glycoprotein of the SARS-CoV-2 Omicron XBB.1.5 variant, encapsulated within lipid nanoparticles (LNPs) to facilitate cellular uptake and antigen expression.[1]

Preclinical studies, primarily in murine models, demonstrated that XBB.1.5-adapted mRNA vaccines induce robust neutralizing antibody responses against the XBB.1.5 variant and show some cross-neutralization against related XBB sublineages and, to a lesser extent, more divergent variants like JN.1.[4] Clinical trials, including Phase 2/3 studies (e.g., NCT04927065) and real-world effectiveness studies, have confirmed the immunogenicity of Andusomeran, showing significant increases in neutralizing antibody titers against XBB.1.5 post-vaccination and providing protection against COVID-19-related hospitalization and medically attended illness.[5] The safety profile of Andusomeran is consistent with that of previous Moderna mRNA COVID-19 vaccines, with common solicited adverse events being mild to moderate and transient.[5]

Andusomeran has received regulatory authorizations, including approvals and Emergency Use Authorizations (EUAs), in numerous regions, including the United States (FDA), Europe (EMA), Canada (Health Canada), Australia (TGA), and the United Kingdom (MHRA), for various age groups starting from 6 months.[2] The development and deployment of variant-adapted vaccines like Andusomeran represent a significant advancement in vaccine technology, enabling more agile responses to rapidly evolving viral pathogens. This capability has been crucial in the ongoing public health strategy to mitigate the impact of the COVID-19 pandemic, though the continuous emergence of new variants underscores the need for ongoing surveillance and potential further vaccine updates.

2. Introduction to Andusomeran (CX-038839 Omicron XBB.1.5 / Spikevax XBB.1.5)

Context: The Evolving SARS-CoV-2 Landscape and the Need for Adapted Vaccines

The COVID-19 pandemic, caused by the Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2), has been characterized by the continuous emergence of viral variants. These variants often possess mutations in the spike (S) protein, the primary target of vaccine-induced immunity, leading to increased transmissibility, altered virulence, or immune evasion capabilities.[4] The Omicron lineage, in particular, and its subsequent sublineages such as BA.1, BA.4/BA.5, XBB (including XBB.1.5, XBB.1.16, XBB.2.3), EG.5.1, BA.2.86, and JN.1, have demonstrated significant antigenic drift, reducing the effectiveness of vaccines based on the ancestral SARS-CoV-2 strain.[4]

This viral evolution necessitated the development of adapted vaccines to broaden and enhance protective immunity against currently circulating and emerging strains. Global health authorities, including the World Health Organization (WHO) and the U.S. Food and Drug Administration (FDA), recommended updating vaccine formulations to target these newer variants, such as the XBB.1.5 sublineage, which became predominant in early 2023.[8] The move towards monovalent XBB.1.5 vaccines, as opposed to earlier bivalent formulations that included an ancestral strain component, was driven by the aim to direct the immune response more specifically towards the dominant circulating variants and potentially mitigate concerns about immune imprinting.[8] Immune imprinting, or original antigenic sin, refers to the phenomenon where the immune system preferentially recalls responses to the first encountered version of an antigen, potentially limiting the breadth or effectiveness of responses to subsequent, antigenically distinct variants. By focusing on a single, more current variant, monovalent vaccines aim to optimize the immune response against the most immediate threat.

Vaccine Identity: Nomenclature and Key Identifiers

The vaccine CX-038839 Omicron (XBB.1.5) is known by several names and identifiers, reflecting its development, regulatory journey, and marketing. Its generic name is Andusomeran.[1] It is a key component of Moderna's updated COVID-19 vaccine strategy.

Table 1: Key Identifiers for Andusomeran (CX-038839 Omicron XBB.1.5)

Identifier Type	Value	Source(s)
Generic Name	Andusomeran	1
DrugBank ID	DB18227	1
Brand Names	Spikevax XBB.1.5, Moderna COVID-19 Vaccine (2023-2024 Formula), Spikevax (2024-2025 Formula)	1
Other Names/Codes	CX-038839 Omicron (XBB.1.5), mRNA-1273.815	1
Type	Biotech, mRNA Vaccine	1
CAS Number	Not explicitly provided for Andusomeran (CX-038839). The CAS number 2918977-08-7, provided in the user query, is associated with Raxtozinameran (Pfizer-BioNTech XBB.1.5 vaccine) in some sources.31	User Query31 (for Raxtozinameran)

Andusomeran is a monovalent mRNA vaccine specifically designed to encode the spike protein of the SARS-CoV-2 Omicron XBB.1.5 subvariant.[1] This targeted approach aims to provide updated protection against this particular strain, which was a significant contributor to COVID-19 cases during its period of prevalence.

3. Development and Manufacturer

Andusomeran (Spikevax XBB.1.5) was developed by Moderna, Inc., a biotechnology company known for its pioneering work in mRNA therapeutics and vaccines.[1] The rapid development of Moderna's COVID-19 vaccines, including the XBB.1.5 adaptation, was built upon foundational research and collaborations. Notably, the initial development of Moderna's COVID-19 vaccine platform involved significant partnerships with U.S. government entities, including the National Institute of Allergy and Infectious Diseases (NIAID), part of the National Institutes of Health (NIH), and the Biomedical Advanced Research and Development Authority (BARDA).[2] These collaborations were instrumental in accelerating research, clinical trials, and manufacturing scale-up, particularly during the early phases of the pandemic. This public-private partnership model has been highlighted as a key factor in the unprecedented speed of COVID-19 vaccine development.

While some documentation, such as product monographs for Comirnaty [17], mentions BioNTech Manufacturing GmbH as a manufacturer, this pertains to the Pfizer-BioNTech COVID-19 vaccine (Raxtozinameran for the XBB.1.5 version) and not Andusomeran/Spikevax XBB.1.5, which is Moderna's product.

4. Mechanism of Action and Pharmacology

Design: Targeting the Omicron XBB.1.5 Spike Protein

Andusomeran is a nucleoside-modified mRNA (modRNA) vaccine.[1] This modification, typically involving the substitution of uridine with N1-methylpseudouridine, helps to reduce innate immunogenicity of the mRNA and enhance protein translation, contributing to a more effective and potentially better-tolerated vaccine.[2] The mRNA sequence in Andusomeran encodes the full-length spike (S) glycoprotein of the SARS-CoV-2 Omicron XBB.1.5 subvariant.[1] To enhance immunogenicity, the encoded spike protein is stabilized in its prefusion conformation, often through specific proline substitutions (e.g., K982P and V983P, as noted for Andusomeran [1]). The prefusion conformation of the spike protein is the primary target for potent neutralizing antibodies; thus, stabilizing it in this form is a critical design strategy to elicit a more effective immune response. This approach is a common feature in many successful COVID-19 vaccines, as it presents the most relevant viral epitopes to the immune system.

The mRNA is encapsulated within lipid nanoparticles (LNPs).[1] These LNPs serve multiple functions: they protect the fragile mRNA from degradation by extracellular enzymes, facilitate its uptake into host cells, and aid in its release into the cytoplasm where protein synthesis occurs.

Cellular Uptake and Antigen Expression

Following intramuscular injection, the LNPs containing the Andusomeran mRNA are taken up by host cells, primarily antigen-presenting cells (APCs) and muscle cells at the injection site.[1] Once inside the cell, the mRNA is released from the LNP into the cytoplasm. The host cell's ribosomal machinery then translates the mRNA sequence into the SARS-CoV-2 Omicron XBB.1.5 spike protein. These newly synthesized spike proteins are then processed and displayed on the surface of the host cells.[1]

Elicitation of Immune Response

The display of the viral spike protein on the cell surface triggers a robust immune response. The immune system recognizes the XBB.1.5 spike protein as foreign, initiating both humoral and cellular immunity.[1]

• Humoral Immunity: B cells are activated to produce neutralizing antibodies specifically targeting the XBB.1.5 spike protein. These antibodies can bind to the virus, preventing it from entering host cells and thereby neutralizing its infectivity.[1]
• Cellular Immunity: T cells, including CD4$^+$ (helper) T cells and CD8$^+$ (cytotoxic) T cells, are also activated. CD4$^+$ T cells play a crucial role in orchestrating the overall immune response, including helping B cells produce antibodies. CD8$^+$ T cells can recognize and kill host cells that are infected with the virus and are expressing viral antigens on their surface.[3]

This multifaceted immune response prepares the body to rapidly and effectively combat future infections with the SARS-CoV-2 XBB.1.5 variant and potentially other closely related sublineages.

Pharmacokinetics/Pharmacodynamics

Specific pharmacokinetic and pharmacodynamic data for Andusomeran are not extensively detailed in the provided sources beyond general characteristics applicable to mRNA vaccines. The mRNA delivered by the vaccine is transiently expressed within host cells; it does not integrate into the host genome and is naturally degraded by cellular processes after protein translation.[3] Similarly, the lipid components of the LNPs are metabolized by the body.[2] The primary pharmacodynamic effect is the induction of an antigen-specific immune response, leading to the generation of neutralizing antibodies and cellular immunity.

5. Preclinical Evaluation

Preclinical studies form a critical part of vaccine development, providing initial data on immunogenicity and safety before human trials commence. For the XBB.1.5-adapted mRNA vaccines, including Andusomeran (mRNA-1273.815), preclinical evaluation typically involves animal models, often mice, to assess these parameters.[4]

While some of the provided snippets detail preclinical findings for Pfizer-BioNTech's BNT162b2 XBB.1.5 vaccine [4], information directly pertaining to Moderna's Andusomeran (mRNA-1273.815) is also available, particularly concerning its immunogenicity in mice against XBB.1.5 and its cross-neutralization capabilities against emerging variants like JN.1 and KP.2.[6] General preclinical safety and toxicology data for the broader mRNA vaccine platform are also relevant.[42]

Animal Models and Immunogenicity:

Studies in BALB/c mice have been instrumental in evaluating the immune response elicited by mRNA-1273.815. These studies assessed neutralizing antibody (nAb) titers against the XBB.1.5 variant and other circulating sublineages.

• When administered as a primary series or a booster dose in mice, mRNA-1273.815 (monovalent XBB.1.5 vaccine) was compared to newer JN.1- or KP.2-matched vaccines.[6]
• The JN.1- and KP.2-matched vaccines elicited robust nAb titers against their respective matched strains and effectively cross-neutralized other JN.1 subvariants (KP.3, LA.2, XEC). However, these newer variant-matched vaccines did not effectively neutralize the antigenically distant XBB.1.5 variant.[6]
• Conversely, while the XBB.1.5 vaccine (mRNA-1273.815) would be expected to induce strong responses against XBB.1.5, these preclinical mouse studies indicated that the nAb responses elicited by the XBB.1.5 vaccine showed limited cross-neutralization against the more divergent JN.1 lineage variants.[6] This finding underscores the concept of antigenic distance; as new variants diverge significantly from the vaccine strain, the breadth of the neutralizing antibody response may diminish.

Preclinical data for the Pfizer-BioNTech XBB.1.5 vaccine (BNT162b2) also showed that it elicited substantially higher serum neutralizing titers against Omicron XBB.1.5 and related sublineages (XBB.1.16, EG.5.1, HV.1) and the phylogenetically distant BA.2.86 lineage compared to the earlier bivalent BA.4/5 vaccine, in both booster and primary series settings in mice.[4] Strong S-specific Th1-biased CD4$^+$ and IFN$\gamma^+$ CD8$^+$ T cell responses were also observed with BNT162b2 XBB.1.5.[4] While from a different manufacturer, these findings for another XBB.1.5 mRNA vaccine provide a general indication of the type of immune responses expected from this class of variant-adapted vaccines.

The continuous evolution of SARS-CoV-2, with new variants rapidly replacing older ones, poses an ongoing challenge for vaccine development. Preclinical immunogenicity studies are vital for rapidly assessing how well an updated vaccine might perform against both its target variant and newly emerging strains. The observation of reduced cross-neutralization by XBB.1.5-induced antibodies against later JN.1 lineage variants in these animal models [6] accurately foreshadowed the need for subsequent vaccine updates to address these newer threats.

Safety/Toxicology:

General preclinical safety data for mRNA vaccines, such as those utilizing the mRNA-1273 platform, have typically shown them to be well-tolerated in animal models, with most effects related to the expected immune response.42 Specific GLP (Good Laboratory Practice) toxicology studies for earlier iterations of Moderna's mRNA vaccines in mice and rats, involving multiple intramuscular doses, generally revealed low toxicity, with observations primarily consistent with normal immunological responses to vaccination. Reproductive toxicity studies in rats for earlier vaccine versions did not show adverse effects on reproductive parameters, delivery, or fetal development at the doses tested.44 While direct preclinical toxicology reports for mRNA-1273.815 are not detailed in the snippets, the safety profile is largely inferred from the extensive data accumulated for the parent mRNA-1273 platform and its previous iterations.

6. Clinical Development Program (mRNA-1273.815 / Andusomeran)

The clinical development of Andusomeran (mRNA-1273.815), Moderna's monovalent COVID-19 vaccine targeting the Omicron XBB.1.5 subvariant, has encompassed Phase 2/3 trials and real-world effectiveness studies to evaluate its immunogenicity, safety, and protective efficacy.

Overview of Key Clinical Trials:

Several studies have provided crucial data on mRNA-1273.815:

1. NCT04927065 (Phase 2/3, Open-Label): This ongoing study evaluated mRNA-1273.815 (50 µg) administered as a fifth dose (third booster) to adults who had previously received a primary series and two prior booster doses, with the last being an Omicron BA.4/BA.5 bivalent vaccine. It assessed immunogenicity against XBB.1.5 and emerging variants, as well as safety over a 6-month period.[5]
2. Real-World Effectiveness (RWE) Observational Cohort Study (US Adults): Utilizing large US medical and pharmacy claims databases (HealthVerity), this study compared adults vaccinated with mRNA-1273.815 to unvaccinated matched individuals to estimate vaccine effectiveness (VE) against COVID-19 hospitalization and medically attended COVID-19 during the 2023-2024 respiratory season.[8]
3. Phase 3 Randomized Study in Japan (mRNA-1283.815 vs. mRNA-1273.815): This study compared a next-generation COVID-19 vaccine candidate (mRNA-1283.815, 10 µg) with mRNA-1273.815 (50 µg), both monovalent XBB.1.5-containing, in individuals aged $\geq$12 years in Japan, assessing immunogenicity and safety.[15]
4. Korean Multicenter Case-Control Study: This study evaluated the effectiveness of the XBB.1.5 monovalent mRNA vaccine in preventing symptomatic COVID-19 in Korea.[8]

Table 2: Summary of Key Clinical Trial Results for Andusomeran (mRNA-1273.815)

Trial Identifier/Type	Phase	Key Population	Intervention (mRNA-1273.815)	Primary Endpoints	Key Results	Source(s)
NCT04927065	Phase 2/3	Adults ($\geq$18 years) previously received 4 mRNA vaccine doses	Single 50 µg booster dose	Safety; Immunogenicity (nAb vs XBB.1.5 & other variants at Day 29)	Safe; 17.5-fold nAb increase vs XBB.1.5 at Day 29 (5.2-fold at 6 months); Lower nAb vs JN.1 lineage	5
RWE Observational Study (US HealthVerity Data)	Observational	Adults ($\geq$18 years)	Single dose (standard of care)	VE vs COVID-19 hospitalization; VE vs medically attended COVID-19	VE vs hospitalization: 51% (95% CI: 48-54%); VE vs medically attended: 25% (95% CI: 24-27%). Median follow-up 84 days.	9
RWE Observational Study (US HealthVerity Data - another report)	Observational	Adults ($\geq$18 years)	Single dose (standard of care)	VE vs COVID-19 hospitalization; VE vs medically attended COVID-19	VE vs hospitalization: 60.2% (95% CI: 53.4-66.0); VE vs medically attended: 33.1% (30.2-35.9). Median follow-up 63 days.	11
Phase 3 Study (Japan)	Phase 3	Individuals $\geq$12 years	Single 50 µg dose	Immunogenicity (nAb vs XBB.1.5 at Day 29); Safety	nAb GMFR vs XBB.1.5: 11.28; Seroresponse rate: 86.8%. Safe and well-tolerated.	15
Korean Case-Control Study	Observational	Patients undergoing COVID-19 testing	Single dose (standard of care)	VE vs symptomatic COVID-19	Adjusted VE: 56.8% (95% CI: 18.7-77.9%) in first 1-2 months	8

Immunogenicity in Humans:

Clinical studies consistently demonstrated that Andusomeran (mRNA-1273.815) elicits robust neutralizing antibody responses against the targeted Omicron XBB.1.5 variant.

• In the Phase 2/3 study (NCT04927065), a 50 µg booster dose of mRNA-1273.815 in adults led to a 17.5-fold increase in nAb geometric mean titers (GMTs) against XBB.1.5 at Day 29 compared to pre-booster levels.[5]
• The Phase 3 study in Japan also showed strong nAb responses to a 50 µg dose of mRNA-1273.815 against XBB.1.5, with a geometric mean fold rise (GMFR) of 11.28 by Day 29.[15]

Regarding cross-neutralizing activity, the NCT04927065 study found that mRNA-1273.815 also induced nAb responses against more divergent variants such as JN.1, JN.1.23, and KP.2, although the GMTs and fold-rises for these variants were lower than those against XBB.1.5 at both Day 29 and Day 181.[5] Preliminary data announced by Moderna in August 2023 also indicated a significant boost in neutralizing antibodies against the then-circulating EG.5 and FL.1.5.1 variants, and earlier data presented to the FDA VRBPAC in June 2023 confirmed robust human immune responses across key XBB strains.[28] The reduced potency against significantly drifted subsequent variants like JN.1 is an important consideration. While the XBB.1.5 vaccine provided a necessary update against the then-dominant strains, the rapid evolution of SARS-CoV-2 means that the breadth of protection against future, antigenically distinct variants can diminish, highlighting the dynamic challenge of vaccine strain selection.

Clinical Efficacy (Real-World Effectiveness):

Real-world evidence has been crucial in assessing the performance of Andusomeran in diverse populations.

• A large observational study using US claims data (HealthVerity) estimated the VE of mRNA-1273.815 against COVID-19 hospitalization at 51% (95% CI: 48–54%) and against medically attended COVID-19 at 25% (95% CI: 24–27%) over a median follow-up of 84 days. VE was noted to decline over time but remained significant.[9] A separate report on similar data with a median follow-up of 63 days showed a VE of 60.2% against hospitalization and 33.1% against medically attended COVID-19.[11]
• Subgroup analyses from these RWE studies indicated continued protection in older adults ($\geq$65 years, VE 56%) and immunocompromised individuals (VE 46%) against hospitalization.[9]
• A Korean case-control study reported an adjusted VE of 56.8% (95% CI: 18.7-77.9%) for the XBB.1.5 monovalent mRNA vaccine against symptomatic COVID-19 during the initial one to two months post-vaccination.[8]

These RWE studies are invaluable as they reflect vaccine performance under real-world conditions, across heterogeneous populations and varying levels of prior immunity from infection or vaccination. The consistent demonstration of significant protection against severe outcomes, such as hospitalization, particularly in vulnerable groups, underscores the public health utility of the updated vaccine, even as the virus evolves and absolute efficacy against any infection may wane or be lower for milder endpoints.

Durability of Immune Response and Protection:

The NCT04927065 study provided insights into the durability of the immune response, with nAb titers against XBB.1.5 remaining 5.2-fold above pre-booster levels at 6 months post-vaccination.5 Real-world VE studies also indicated that while protection against medically attended COVID-19 and hospitalization declined over time, it remained statistically significant during the observation periods (up to approximately 4 months).9

7. Safety and Tolerability Profile

The safety and tolerability of Andusomeran (mRNA-1273.815) have been evaluated in clinical trials, and its profile is generally consistent with that of previous Moderna mRNA COVID-19 vaccines.

Table 3: Overview of Common Adverse Events Associated with Andusomeran (mRNA-1273.815)

Adverse Event Category	Common Solicited Local AEs	Common Solicited Systemic AEs	Source(s)
mRNA-1273.815 (50 µg)	Injection site pain, erythema (redness), swelling, axillary swelling/tenderness	Fatigue, headache, myalgia, arthralgia, chills, nausea/vomiting, fever	15 (Japan Ph3 Data)25 (General XBB.1.5 vaccine data)

Note: Data primarily from the Japanese Phase 3 study comparing mRNA-1283.815 to mRNA-1273.815. [31] provides AE data for Comirnaty XBB.1.5, which may offer a general reference for XBB.1.5 vaccine AEs.

Reactogenicity:

Clinical trial data from the Phase 3 study in Japan indicated that solicited adverse reactions (ARs) for mRNA-1273.815 (50 µg dose) were common but generally mild to moderate and transient.15

• Solicited Local Adverse Reactions: The most frequently reported local AR was injection site pain. Other local reactions included erythema (redness), swelling (hardness), and axillary swelling or tenderness.[15] In the Japanese Phase 3 study, 95.7% of mRNA-1273.815 recipients reported any solicited local AR within 7 days.[15]
• Solicited Systemic Adverse Reactions: Common systemic ARs included fatigue, headache, myalgia (muscle pain), arthralgia (joint pain), chills, nausea/vomiting, and fever.[15] In the Japanese Phase 3 study, a high percentage of participants also reported systemic ARs, with a median duration of 3 to 4 days.[15]

The reactogenicity profile observed for mRNA-1273.815 is in line with what has been reported for previous iterations of the Moderna mRNA COVID-19 vaccine (Spikevax).[5]

Serious Adverse Events (SAEs) and Adverse Events of Special Interest (AESIs):

• In the NCT04927065 Phase 2/3 study, through 6 months of follow-up for the mRNA-1273.815 arm, no vaccine-related deaths, Serious Adverse Events (SAEs), Medically Attended Adverse Events (MAAEs), AEs leading to withdrawal, or Adverse Events of Special Interest (AESIs) were reported.[5]
• Similarly, in the Japanese Phase 3 study, no SAEs, severe unsolicited AEs, AEs leading to study discontinuation, or deaths were reported in the mRNA-1273.815 group within 28 days after vaccination.[15]
• Myocarditis and Pericarditis: It is important to note that there is a known increased risk of myocarditis (inflammation of the heart muscle) and pericarditis (inflammation of the lining outside the heart) following vaccination with Spikevax products, including adapted versions. These conditions typically develop within a few days and primarily within 14 days after vaccination.[20] Healthcare providers are advised to be alert to the signs and symptoms of myocarditis and pericarditis. This general warning applies to all Spikevax vaccines, and continued pharmacovigilance for these rare events is essential for all formulations, including Andusomeran.

The consistency of Andusomeran's safety profile with that of earlier Spikevax versions is an important finding. It suggests that the adaptation of the mRNA sequence to target the XBB.1.5 variant did not introduce new, unexpected safety concerns regarding common reactogenicity. Nevertheless, the known rare risks associated with mRNA vaccines, such as myocarditis and pericarditis, necessitate ongoing monitoring as the vaccine is deployed in large and diverse populations.

8. Dosage, Administration, and Formulation

Recommended Dosage Regimen:

The dosage and administration schedule for Andusomeran (Spikevax XBB.1.5) vary by age group and, in some cases, prior vaccination or infection history, reflecting efforts to tailor vaccination for optimal immune response and safety across different populations.

• Individuals 12 Years of Age and Older: A single 0.5 mL dose (containing 50 micrograms of andusomeran mRNA from the 0.1 mg/mL dispersion) is recommended, irrespective of previous COVID-19 vaccination history.[18]
• Children 5 Years to <12 Years of Age: A single 0.25 mL dose (containing 25 micrograms of andusomeran mRNA from the 0.1 mg/mL dispersion) is recommended, irrespective of previous COVID-19 vaccination history. If previously vaccinated, this dose should be administered $\geq$2 months after the last previous dose of any COVID-19 vaccine.[18]
• Children 6 Months to 4 Years of Age:
• Without prior vaccination or known history of SARS-CoV-2 infection: Two 0.25 mL doses (25 micrograms mRNA each), with the second dose administered 28 days after the first.[18]
• With prior vaccination or known history of SARS-CoV-2 infection: A single 0.25 mL dose (25 micrograms mRNA) is recommended, administered at least 3 months after the most recent dose of a COVID-19 vaccine.[18]
• Immunocompromised Individuals: Individuals aged 6 months and older with certain kinds of immunocompromise may receive additional doses of an age-appropriate 2023-2024 formula vaccine. The timing and number of additional doses may be based on the individual's clinical circumstances and at the discretion of the healthcare provider, typically with an interval of at least 2 months following the last COVID-19 vaccine dose.[3]

These age-specific dosing regimens and schedules are critical for ensuring both safety and efficacy, as the immune response to vaccination can vary significantly with age and immune status. The provision for additional doses in immunocompromised individuals acknowledges their potential for a suboptimal response to standard vaccination schedules.

Route of Administration:

Andusomeran is administered by intramuscular (IM) injection.1 The preferred site is the deltoid muscle of the upper arm for older children, adolescents, and adults, or the anterolateral aspect of the thigh for infants and younger children.3

Vaccine Presentation and Storage:

• Formulation: Andusomeran is provided as a white to off-white dispersion for injection.[1] The vaccine does not contain preservatives.[46] Each 0.5 mL dose of Spikevax XBB.1.5 (0.1 mg/mL) contains 50 micrograms of andusomeran mRNA embedded in SM-102 lipid nanoparticles.[22]
• Vial Presentations: The vaccine is typically supplied in multidose vials. For example, Spikevax XBB.1.5 0.1 mg/mL is available in a multidose vial that contains 5 doses of 0.5 mL each or 10 doses of 0.25 mL each.[22] Different cap colors or label borders may be used to distinguish formulations intended for different age groups, similar to practices with other COVID-19 vaccines.[17]
• Storage and Handling: Unopened vials are typically stored frozen. Once thawed, they can be stored at refrigerator temperatures (2°C to 8°C) for a limited period (e.g., up to 10 weeks for Comirnaty Omicron XBB.1.5, not exceeding the printed expiry date [32]; Spikevax (original) could be stored refrigerated for up to 30 days prior to first use [46]). Once thawed, the vaccine should not be re-frozen.[32] After the first dose has been withdrawn from a multidose vial, specific time limits for use at room or refrigerated temperature apply (e.g., within 12 hours for Spikevax (original) [46]). Detailed instructions regarding thawing, handling, and disposal are provided in the product-specific monographs.[20]

9. Global Regulatory Status

Andusomeran (Spikevax XBB.1.5 / CX-038839 Omicron XBB.1.5) has received authorizations from major regulatory agencies worldwide, reflecting a global effort to provide updated protection against the evolving SARS-CoV-2 virus.

Table 4: Summary of Global Regulatory Authorizations for Andusomeran (CX-038839 Omicron XBB.1.5)

Regulatory Agency	Country/Region	Authorization Status (Product Name)	Date of Authorization/Approval (XBB.1.5 version)	Indicated Age Groups (XBB.1.5 version)	Source(s)
FDA (Food and Drug Administration)	USA	Approved (Spikevax 2023-2024 Formula); EUA (Moderna COVID-19 Vaccine, 2023-2024 Formula)	September 2023	$\geq$12 years (Approval); 6 months - 11 years (EUA)	2
EMA (European Medicines Agency)	European Union	Authorized (Spikevax XBB.1.5, andusomeran)	Referenced as authorized; specific date not in snippets for XBB.1.5, but original Spikevax authorized Jan 2021, adapted versions followed.	$\geq$6 months (dose varies by age and history)	3
Health Canada	Canada	Authorized (SPIKEVAX XBB.1.5, andusomeran)	September 12, 2023	$\geq$6 months	17
TGA (Therapeutic Goods Administration)	Australia	Registered (SPIKEVAX XBB.1.5, andusomeran)	October 10, 2023 (ARTG listing date)	$\geq$12 years (as per product name on ARTG entry)	24
MHRA (Medicines and Healthcare products Regulatory Agency)	United Kingdom	Approved (Spikevax XBB.1.5, andusomeran)	September 2023	$\geq$6 months	2

Key Aspects of Authorizations:

• United States (FDA): In September 2023, the FDA approved the updated monovalent XBB.1.5 vaccine (Spikevax 2023-2024 formula) for individuals 12 years of age and older. Simultaneously, it was authorized under Emergency Use Authorization (EUA) for individuals aged 6 months through 11 years.[2]
• Europe (EMA): Spikevax XBB.1.5 (andusomeran) is authorized for use in individuals from 6 months of age. The dosing schedule for children aged 6 months to 4 years depends on prior vaccination or infection history, while a single injection is recommended for those aged 5 years and older, irrespective of previous vaccination history.[3] The EMA's authorization process involves a thorough assessment of quality, safety, and efficacy data.
• Canada (Health Canada): SPIKEVAX XBB.1.5 (andusomeran) was authorized on September 12, 2023, for active immunization in individuals 6 months of age and older.[17]
• Australia (TGA): SPIKEVAX XBB.1.5 (andusomeran) COVID-19 VACCINE 0.1 mg/mL suspension for injection vial - single-dose was entered into the Australian Register of Therapeutic Goods (ARTG) on October 10, 2023, indicated for individuals 12 years of age and older.[24]
• United Kingdom (MHRA): The MHRA approved the Moderna (Spikevax) XBB.1.5 vaccine in September 2023 for use in adults and children aged 6 months and older.[2]

The widespread and relatively synchronized authorizations of XBB.1.5-adapted vaccines by these major regulatory bodies underscore a global consensus on the need for updated vaccine formulations to combat the evolving SARS-CoV-2 virus. While specific age indications and authorization pathways (e.g., full approval versus emergency use) may vary slightly by region due to national policies or the timing of data submissions, the overarching goal has been to make these updated vaccines available to protect populations against the dominant circulating variants. This coordinated international response has been a hallmark of the global effort to manage the COVID-19 pandemic.

10. Comparative Context

Direct head-to-head clinical trials comparing Andusomeran (Moderna XBB.1.5) with other XBB.1.5-adapted vaccines from different manufacturers are generally limited in the provided data. However, some context can be drawn from network meta-analyses and studies comparing different vaccine platforms.

A systematic review and feasibility assessment for a network meta-analysis (NMA) of Omicron-adapted COVID-19 vaccines identified 16 studies for XBB formulations, with eight (all mRNA formulations) included in NMAs. This analysis, involving 29.9 million participants, found that BNT162b2 (Pfizer-BioNTech) had the largest evidence base. Comparisons between XBB.1.5-adapted BNT162b2 (Comirnaty) and mRNA-1273 (Spikevax, which Andusomeran is a version of) indicated that both vaccines are effective and comparable against XBB-related hospitalizations, infections, and medically attended visits in adults. Among the elderly, the estimated effectiveness against XBB-related hospitalizations numerically favored BNT162b2, although the NMA was limited by assumptions on effect modifiers and sparse evidence networks.[47] Such NMAs attempt to provide indirect comparisons but are subject to inherent limitations due to differences in study populations, methodologies, and potential unmeasured confounders across the included studies.

Another study focused on the Novavax COVID-19 vaccine, NVX-CoV2601, which is a recombinant spike protein vaccine. This Phase 2/3 study (2019nCoV-313) evaluated NVX-CoV2601 (XBB.1.5 formulation) as a heterologous booster in adults previously vaccinated with three or more mRNA vaccine doses. The results showed that NVX-CoV2601 produced superior neutralizing antibody (nAb) responses to XBB.1.5 compared to the historical comparator group that received NVX-CoV2373 (prototype vaccine). Specifically, the baseline-adjusted nAb GMT for NVX-CoV2601 against XBB.1.5 was 905.9, while for NVX-CoV2373 it was 156.6, resulting in a GMT ratio of 5.8 (95% CI 4.9-6.9).[48] While this study demonstrates strong immunogenicity for the Novavax XBB.1.5 vaccine, it does not directly compare it to Andusomeran within the same trial.

The development of multiple vaccine platforms (mRNA, protein subunit) adapted to the XBB.1.5 variant provided diverse options for public health programs. While direct comparative efficacy data from large, randomized trials are scarce, the available immunogenicity data and real-world effectiveness studies suggest that different XBB.1.5-adapted vaccines can elicit protective immune responses. The subtle differences observed in NMAs or specific population subgroups warrant further investigation but generally support the utility of the available updated vaccines.

11. Conclusion and Future Perspectives

Andusomeran (CX-038839 Omicron XBB.1.5 / Spikevax XBB.1.5) represents a critical adaptation in the ongoing global COVID-19 vaccination strategy, specifically developed by Moderna to address the Omicron XBB.1.5 subvariant. Its mRNA-based platform allowed for rapid modification from earlier vaccine versions, underscoring the agility of this technology in responding to viral evolution.[1] Clinical and real-world data have demonstrated that Andusomeran elicits robust neutralizing antibody responses against the XBB.1.5 strain and provides significant protection against COVID-19-related hospitalization and medically attended illness, particularly in vulnerable populations.[5] The safety profile of Andusomeran is consistent with that of prior Moderna mRNA vaccines, characterized mainly by transient local and systemic reactogenicity.[5]

The global regulatory authorizations for Andusomeran across various age groups highlight its importance as a public health tool.[2] However, the continuous and rapid evolution of SARS-CoV-2, with the emergence of newer variants such as JN.1 and its descendants (e.g., KP.2, KP.3, LA.2), presents an ongoing challenge.[4] Preclinical and clinical immunogenicity data indicate that while the XBB.1.5-adapted vaccines provide a good response against XBB lineage viruses, their cross-neutralizing capacity against significantly drifted subsequent variants like JN.1 is reduced.[5] This "antigenic chase" necessitates ongoing genomic surveillance and a flexible vaccine development strategy.

The experience with Andusomeran and other variant-adapted vaccines has matured the pandemic response framework. It has demonstrated that vaccine technology can indeed adapt with relative speed. Nevertheless, the strategy of sequentially updating monovalent vaccines to match dominant circulating strains may face limitations in providing sustained, broadly protective immunity against a rapidly diversifying virus. This situation emphasizes the critical need for continued research into next-generation vaccine approaches. These may include strategies aimed at eliciting broader, more durable protection against a wider range of sarbecoviruses or future SARS-CoV-2 variants, potentially through targeting more conserved viral epitopes or inducing different arms of the immune system more effectively. The journey with Andusomeran underscores both the remarkable achievements of mRNA vaccine technology and the formidable challenge posed by highly mutable respiratory viruses.

References

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• [9] Lin, D. Y., et al. (2025). Evaluating the Effectiveness of mRNA-1273.815 Against COVID-19 Hospitalization Among Adults Aged ≥ 18 Years in the United States. Infectious Diseases and Therapy, 14(1), 199-216. [9]
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• [38] Moderna, Inc. (2021, October 25). Moderna Announces Positive Top Line Data from Phase 2/3 Study of COVID-19 Vaccine in Children 6 to 11 Years of Age [Press release]. Retrieved from https://investors.modernatx.com/news/news-details/2021/Moderna-Announces-Positive-Top-Line-Data-from-Phase-23-Study-of-COVID-19-Vaccine-in-Children-6-to-11-Years-of-Age/default.aspx (Relates to original mRNA-1273 in children)
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• [55] Ali, K., et al. (2022). Evaluation of mRNA-1273 Covid-19 Vaccine in Children 6 to 11 Years of Age. The New England Journal of Medicine, 386(21), 2003-2014. [52]
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• [9] Lin, D. Y., et al. (2025). Evaluating the Effectiveness of mRNA-1273.815 Against COVID-19 Hospitalization Among Adults Aged ≥ 18 Years in the United States. Infectious Diseases and Therapy, 14(1), 199-216. [9]
• [34] Moderna, Inc. (2023, September 13). Moderna Expands the Field of mRNA Medicine with Positive Clinical Results Across Cancer, Rare Disease, and Infectious Disease [Press release]. [34]
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• [12] Link-Gelles, R., et al. (2024). Effectiveness of the 2023–2024 Omicron XBB.1.5-containing mRNA COVID-19 Vaccine (mRNA-1273.815) in Preventing COVID-19–related Hospitalizations and Medical Encounters Among Adults in the United States. Open Forum Infectious Diseases, 11(12), ofae695. [11]
• [14] Priddy, F. H., et al. (2024). P-102. Six-Month Safety, Durability, and Cross-Neutralization of the SARS-CoV-2 XBB.1.5-Containing Vaccine. Open Forum Infectious Diseases, 12(Supplement_1), ofae631.309. [14]
• [15] Moderna, Inc. (2025, April 14). Immunogenicity and Safety of a SARS-CoV-2 N-Terminal Domain and Receptor-Binding Domain Monovalent XBB.1.5 Vaccine in Japanese Participants (mRNA-1283.815 vs mRNA-1273.815) [Poster Presentation]. [15]
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The snippets are highly redundant for this query as many point to the same studies or regulatory information. I will synthesize carefully to avoid repetition while ensuring comprehensive coverage.# Andusomeran (CX-038839 Omicron XBB.1.5): A Comprehensive Report on the Monovalent COVID-19 mRNA Vaccine

1. Executive Summary

CX-038839 Omicron (XBB.1.5), known by the generic name Andusomeran and marketed as Spikevax XBB.1.5, is a monovalent messenger RNA (mRNA) vaccine developed by Moderna. This vaccine is specifically designed to elicit a protective immune response against the XBB.1.5 subvariant of the SARS-CoV-2 Omicron lineage, a strain that was predominant during the vaccine's development and deployment period.[1] Andusomeran utilizes nucleoside-modified mRNA technology, encoding the prefusion-stabilized spike (S) glycoprotein of the SARS-CoV-2 Omicron XBB.1.5 variant. This mRNA is encapsulated within lipid nanoparticles (LNPs) to ensure efficient delivery into host cells and subsequent antigen expression.[1]

Preclinical investigations, primarily conducted in murine models, indicated that XBB.1.5-adapted mRNA vaccines, such as Andusomeran, induce robust neutralizing antibody responses against the XBB.1.5 variant. These studies also explored cross-neutralization capabilities against related XBB sublineages and, to a lesser extent, more antigenically distant variants like JN.1.[4] Subsequent human clinical trials, including Phase 2/3 studies (e.g., NCT04927065) and extensive real-world effectiveness analyses, have corroborated the immunogenicity of Andusomeran. These studies have demonstrated significant increases in neutralizing antibody titers against XBB.1.5 following vaccination and have provided evidence of protection against COVID-19-related hospitalization and medically attended illness.[5] The safety profile of Andusomeran has been found to be consistent with that of previous iterations of Moderna's mRNA COVID-19 vaccines, with the most commonly reported solicited adverse events being mild to moderate and transient in nature.[5]

Andusomeran has secured regulatory authorizations, including full approvals and Emergency Use Authorizations (EUAs), from major health authorities globally. These include the U.S. Food and Drug Administration (FDA), the European Medicines Agency (EMA), Health Canada, the Australian Therapeutic Goods Administration (TGA), and the UK's Medicines and Healthcare products Regulatory Agency (MHRA). Authorizations typically cover various age groups, often starting from 6 months of age.[2] The rapid development and global deployment of variant-adapted vaccines like Andusomeran signify a notable advancement in vaccine technology, permitting more agile and timely responses to the challenges posed by rapidly evolving viral pathogens. This capability has proven essential in the ongoing public health strategies to mitigate the global impact of the COVID-19 pandemic. Nevertheless, the continuous emergence of new SARS-CoV-2 variants underscores the persistent need for ongoing genomic surveillance and potentially further refinements in vaccine design and composition.

2. Introduction to Andusomeran (CX-038839 Omicron XBB.1.5 / Spikevax XBB.1.5)

Context: The Evolving SARS-CoV-2 Landscape and the Need for Adapted Vaccines

The COVID-19 pandemic, initiated by SARS-CoV-2, has been marked by the continuous genetic evolution of the virus, leading to the emergence of numerous variants of concern and variants of interest. These variants frequently harbor mutations in the spike (S) protein, which is the primary antigenic target for vaccine-induced immunity. Such mutations can confer advantages to the virus, including increased transmissibility, altered disease severity, or the ability to evade host immune responses generated by prior infection or vaccination.[4] The Omicron lineage (B.1.1.529) and its subsequent sublineages, such as BA.1, BA.2, BA.4/BA.5, and particularly the XBB family (including XBB.1.5, XBB.1.16, XBB.2.3), followed by EG.5.1, BA.2.86, and the JN.1 lineage, have exhibited significant antigenic drift. This drift has led to a reduction in the effectiveness of vaccines based on the ancestral SARS-CoV-2 strain or earlier Omicron variants.[4]

The dynamic nature of SARS-CoV-2 evolution necessitated the adaptation of COVID-19 vaccines to better match currently circulating strains, thereby aiming to broaden and enhance protective immunity. Consequently, global health authorities such as the World Health Organization (WHO) and national regulatory bodies like the U.S. Food and Drug Administration (FDA) recommended updating vaccine formulations to specifically target predominant variants, such as the Omicron XBB.1.5 subvariant, which gained global ascendancy in early 2023.[8] The strategic shift towards monovalent XBB.1.5 vaccines, as opposed to earlier bivalent formulations that included an ancestral Wuhan strain component alongside an Omicron component, was influenced by several factors. A key consideration was the desire to direct the immune response more precisely towards the currently most relevant antigenic targets. Furthermore, there were discussions regarding immune imprinting, a phenomenon where initial exposure to a specific viral antigen (e.g., from the ancestral strain vaccine) might preferentially shape subsequent immune responses, potentially limiting the breadth or magnitude of the response to newer, antigenically distinct variants when both are presented in a bivalent vaccine.[8] A monovalent vaccine formulation aims to circumvent this by focusing the immune response solely on the updated variant component.

Vaccine Identity: Nomenclature and Key Identifiers

The COVID-19 vaccine CX-038839 Omicron (XBB.1.5) is primarily identified by its generic name, Andusomeran.[1] It is a monovalent mRNA vaccine developed by Moderna to target the Omicron XBB.1.5 subvariant of SARS-CoV-2. The vaccine is marketed under various brand names, most notably Spikevax XBB.1.5 or as part of Moderna's seasonally updated COVID-19 vaccine formulations.

Table 1: Key Identifiers for Andusomeran (CX-038839 Omicron XBB.1.5)

Identifier Type	Value	Source(s)
Generic Name	Andusomeran	1
DrugBank ID	DB18227	1
Brand Names	Spikevax XBB.1.5, Moderna COVID-19 Vaccine (2023-2024 Formula), Spikevax (2024-2025 Formula)	1
Other Names/Codes	CX-038839 Omicron (XBB.1.5), mRNA-1273.815	1
Type	Biotech, mRNA Vaccine	1
CAS Number	Not explicitly provided for Andusomeran (CX-038839). The CAS number 2918977-08-7, listed in the user query, is associated with Raxtozinameran (Pfizer-BioNTech XBB.1.5 vaccine) in some sources.	User Query31 (for Raxtozinameran)

Andusomeran, as a monovalent formulation, contains mRNA encoding only the spike protein of the SARS-CoV-2 Omicron XBB.1.5 subvariant.[1] This targeted design aims to provide updated and focused protection against this specific and previously dominant viral strain. The consistent use of DrugBank ID DB18227 and the name Andusomeran or CX-038839 in relation to Moderna's XBB.1.5 vaccine helps in its precise identification amidst various vaccine products. The CAS number discrepancy noted in the table highlights the importance of cross-referencing multiple identifiers for accurate drug information retrieval.

3. Development and Manufacturer

Andusomeran, marketed as Spikevax XBB.1.5, was developed by Moderna, Inc., a U.S.-based biotechnology company specializing in mRNA therapeutics and vaccines.[1] Moderna has been at the forefront of mRNA vaccine technology, and its COVID-19 vaccine platform was one of the first to receive authorization globally.

The rapid development of Moderna's initial COVID-19 vaccine (mRNA-1273, based on the ancestral SARS-CoV-2 strain) and subsequent variant-adapted versions like Andusomeran was significantly aided by collaborations, particularly in the early stages of the pandemic response. Key partnerships included those with U.S. government agencies such as the National Institute of Allergy and Infectious Diseases (NIAID), a part of the National Institutes of Health (NIH), and the Biomedical Advanced Research and Development Authority (BARDA), part of the Office of the Assistant Secretary for Preparedness and Response at the U.S. Department of Health and Human Services.[2] These collaborations provided crucial financial and logistical support, facilitating accelerated research, large-scale clinical trials, and the rapid scale-up of manufacturing capabilities. This public-private partnership model has been recognized as a critical element in the swift delivery of COVID-19 vaccines.

While some product monographs for COVID-19 vaccines, such as Comirnaty, list BioNTech Manufacturing GmbH as a manufacturer [17], it is important to distinguish that this pertains to the Pfizer-BioNTech COVID-19 vaccine. Andusomeran (Spikevax XBB.1.5) is a distinct product developed and primarily manufactured by Moderna and its contracted manufacturing organizations.

4. Mechanism of Action and Pharmacology

Design: Targeting the Omicron XBB.1.5 Spike Protein

Andusomeran is a nucleoside-modified messenger RNA (mRNA) vaccine.[1] The mRNA technology involves synthesizing a strand of mRNA that carries the genetic instructions for producing a specific viral antigen. In the case of Andusomeran, the mRNA sequence encodes the full-length spike (S) glycoprotein of the SARS-CoV-2 Omicron XBB.1.5 subvariant.[1] The S protein is crucial for viral entry into host cells and is the primary target for neutralizing antibodies.

A key feature of the encoded S protein in Andusomeran is its stabilization in the prefusion conformation. This is typically achieved through specific amino acid substitutions, such as the K982P and V983P mutations mentioned for Andusomeran [1], which lock the S protein in the shape it adopts before fusing with a host cell. The prefusion conformation is considered more immunogenic as it presents critical epitopes that elicit potent neutralizing antibody responses. This design strategy, aimed at maximizing the quality and quantity of the protective immune response, is a common characteristic of several advanced COVID-19 vaccines.

The mRNA molecule is encapsulated within lipid nanoparticles (LNPs).[1] These LNPs are essential for protecting the mRNA from degradation by enzymes in the body and for facilitating its efficient uptake into host cells after administration.

Cellular Uptake and Antigen Expression

Following intramuscular injection, the LNPs carrying the Andusomeran mRNA are taken up by host cells, including muscle cells at the injection site and antigen-presenting cells (APCs) such as dendritic cells and macrophages.[1] Once inside the cell, the mRNA is released from the LNP into the cytoplasm. The host cell's own protein-synthesizing machinery (ribosomes) then reads the mRNA instructions and produces the SARS-CoV-2 Omicron XBB.1.5 spike protein. These newly synthesized spike proteins are subsequently processed by the cell and displayed on its surface, mimicking a natural viral infection without causing disease.[1]

Elicitation of Immune Response

The presentation of the XBB.1.5 spike protein on the surface of host cells alerts the immune system, triggering a coordinated adaptive immune response comprising both humoral and cellular immunity.[1]

• Humoral Immunity: B lymphocytes recognize the foreign spike protein and, with the help of CD4$^+$ T helper cells, differentiate into plasma cells that produce neutralizing antibodies. These antibodies are specific to the XBB.1.5 spike protein and can bind to the virus, blocking its entry into host cells and thereby preventing infection or reducing its severity.[1] Memory B cells are also generated, providing long-term potential for rapid antibody production upon re-exposure to the virus.
• Cellular Immunity: T lymphocytes are also activated. CD4$^+$ T helper cells play a crucial role in orchestrating the adaptive immune response, including supporting B cell activation and antibody production, and promoting the development of CD8$^+$ cytotoxic T cells. CD8$^+$ T cells can identify and destroy host cells that are infected with SARS-CoV-2 and are expressing viral antigens (including the spike protein) on their surface, thereby helping to clear the infection.[3] Memory T cells are also formed, contributing to long-term protection.

This dual humoral and cellular immune response primes the body to recognize and rapidly combat future encounters with the SARS-CoV-2 XBB.1.5 variant and potentially closely related sublineages.

Pharmacokinetics/Pharmacodynamics

The mRNA within the vaccine is utilized by the host cell's machinery for a limited period to produce the spike protein. The mRNA itself does not integrate into the host cell's DNA and is naturally degraded by normal cellular processes relatively quickly after protein translation is complete.[3] The lipid components of the LNPs are also metabolized and cleared by the body through natural pathways.[2] The primary pharmacodynamic effect of Andusomeran is the induction of a specific and protective immune response against the SARS-CoV-2 XBB.1.5 spike protein.

5. Preclinical Evaluation

Preclinical studies are fundamental in the vaccine development pipeline, providing initial assessments of immunogenicity and safety in animal models before progression to human clinical trials. For XBB.1.5-adapted mRNA vaccines like Andusomeran (mRNA-1273.815), these studies typically involve murine models to evaluate the vaccine's ability to elicit neutralizing antibody responses and T-cell activity against the target variant and assess potential cross-protection against other circulating strains.[4]

While some detailed preclinical reports in the provided information pertain to the Pfizer-BioNTech XBB.1.5 vaccine (BNT162b2) [4], specific preclinical data for Moderna's Andusomeran (mRNA-1273.815) are also mentioned, particularly in the context of its immunogenicity against XBB.1.5 and its comparative performance against newer variants like JN.1 and KP.2 in mouse models.[6] General safety and toxicology findings from the broader mRNA vaccine platform also inform the preclinical understanding of Andusomeran.[42]

Animal Models and Immunogenicity:

Studies conducted in BALB/c mice have been pivotal for characterizing the immune responses induced by mRNA-1273.815. These experiments assessed:

• Neutralizing Antibody (nAb) Titers against XBB.1.5: When administered as a primary series or as a booster, mRNA-1273.815 (monovalent XBB.1.5) was evaluated for its capacity to generate nAbs against the XBB.1.5 variant.[6]
• Cross-Neutralization against Other Variants: The ability of antibodies induced by mRNA-1273.815 to neutralize other co-circulating or emerging variants (e.g., EG.5.1, BA.2.86, and particularly the antigenically distant JN.1 lineage variants like KP.2, KP.3, LA.2, XEC) was a key area of investigation. Preclinical studies comparing mRNA-1273.815 with vaccines matched to JN.1 or KP.2 showed that while mRNA-1273.815 induced robust responses against XBB.1.5, its cross-neutralizing capacity against the JN.1 lineage was limited. Conversely, the JN.1- and KP.2-matched vaccines showed strong neutralization of their respective strains and related JN.1 subvariants but did not effectively neutralize XBB.1.5.[6] This highlights the specificity of the immune response generated by variant-matched vaccines and the challenges posed by significant antigenic drift.

The Pfizer-BioNTech XBB.1.5 vaccine (BNT162b2) also demonstrated in preclinical mouse models that it elicited substantially higher nAb titers against Omicron XBB.1.5 and related sublineages (XBB.1.16, EG.5.1, HV.1) as well as the BA.2.86 lineage, compared to the earlier bivalent BA.4/5 vaccine. These studies also reported strong S-specific Th1-biased CD4$^+$ and IFN$\gamma^+$ CD8$^+$ T-cell responses.[4] These findings, though from a different mRNA vaccine, provide a general indication of the immunological profile expected from XBB.1.5-adapted mRNA vaccines.

The continuous evolution of SARS-CoV-2 necessitates such preclinical evaluations to rapidly assess the potential effectiveness of updated vaccine candidates against new threats. The observed patterns of neutralization, particularly the reduced cross-reactivity against highly drifted variants, are critical for informing public health strategies and decisions regarding subsequent vaccine strain updates. This dynamic interplay between viral evolution and vaccine adaptation underscores the "antigenic chase" that has characterized the COVID-19 pandemic response.

Safety/Toxicology:

General preclinical safety data for the mRNA vaccine platform, upon which Andusomeran is based, have consistently shown good tolerability in animal models. Most observed effects are typically related to the expected inflammatory and immune responses associated with vaccination, rather than specific organ toxicity.42 For instance, Good Laboratory Practice (GLP) toxicology studies on earlier iterations of Moderna's mRNA vaccines in mice and rats, involving multiple intramuscular doses, generally indicated low toxicity. Reproductive toxicity studies in rats for these earlier vaccine versions did not reveal adverse effects on fertility, maternal health, or fetal development at the doses tested.44 While specific, detailed preclinical toxicology reports for mRNA-1273.815 are not exhaustively covered in the provided snippets, its safety profile is largely extrapolated from the extensive data accumulated for the parent mRNA-1273 platform and its various iterations.

6. Clinical Development Program (mRNA-1273.815 / Andusomeran)

The clinical development of Andusomeran (mRNA-1273.815), Moderna's monovalent COVID-19 vaccine targeting the Omicron XBB.1.5 subvariant, has involved Phase 2/3 clinical trials and real-world effectiveness studies to rigorously evaluate its immunogenicity, safety, and protective efficacy in human populations.

Overview of Key Clinical Trials:

Several key studies have provided data on mRNA-1273.815:

1. NCT04927065 (Phase 2/3, Open-Label): This ongoing study is a cornerstone for evaluating mRNA-1273.815. It assessed the vaccine (50 µg) when administered as a fifth dose (third booster) to adults who had a history of prior COVID-19 vaccination, including an Omicron BA.4/BA.5 bivalent booster. The study focused on immunogenicity against XBB.1.5 and other emerging variants, alongside safety monitoring over a 6-month period.[5]
2. Real-World Effectiveness (RWE) Observational Cohort Studies (US Adults): Multiple analyses using large U.S. administrative claims databases (e.g., HealthVerity) have been conducted. These studies compared adults vaccinated with mRNA-1273.815 to matched unvaccinated individuals to estimate vaccine effectiveness (VE) against outcomes like COVID-19-related hospitalization and medically attended COVID-19 during the 2023-2024 respiratory season.[8]
3. Phase 3 Randomized Study in Japan (mRNA-1283.815 vs. mRNA-1273.815): This trial compared a next-generation COVID-19 vaccine candidate (mRNA-1283.815, 10 µg) with mRNA-1273.815 (50 µg), both being monovalent XBB.1.5-containing formulations. The study, conducted in individuals aged $\geq$12 years in Japan, provided comparative immunogenicity and safety data for mRNA-1273.815.[15]
4. Korean Multicenter Test-Negative Case-Control Study: This study aimed to evaluate the effectiveness of the XBB.1.5 monovalent mRNA vaccine in preventing symptomatic COVID-19 within the South Korean population.[8]
5. Moderna Clinical Trial mRNA-1273-P401 (NCT05933304): Titled "A Study of an Investigational mRNA-1273.815 COVID-19 Vaccine in Previously Vaccinated Adults," this Phase 3, randomized, observer-blind, active-controlled trial was designed to assess the immunogenicity of mRNA-1273.815 in adults who had been previously vaccinated.[35]

Table 2: Summary of Key Clinical Trial Results for Andusomeran (mRNA-1273.815)

Trial Identifier/Type & Region	Phase	Key Population	Intervention (mRNA-1273.815)	Primary Endpoints	Key Results	Source(s)
NCT04927065 (Global)	Phase 2/3	Adults ($\geq$18 yrs), 4 prior mRNA vaccine doses	Single 50 µg booster	Safety; Immunogenicity (nAb vs XBB.1.5 & other variants at Day 29)	Safe; 17.5-fold nAb increase vs XBB.1.5 at Day 29 (5.2-fold at 6 months); Lower nAb vs JN.1 lineage.	5
RWE Observational Study (US HealthVerity Data)	Observational	Adults ($\geq$18 yrs)	Single dose (standard of care)	VE vs COVID-19 hospitalization; VE vs medically attended COVID-19	VE vs hospitalization: 51% (95% CI: 48-54%); VE vs medically attended: 25% (95% CI: 24-27%). Median follow-up 84 days. VE declined over time but remained significant.	9
RWE Observational Study (US HealthVerity Data - Alt. Report)	Observational	Adults ($\geq$18 yrs)	Single dose (standard of care)	VE vs COVID-19 hospitalization; VE vs medically attended COVID-19	VE vs hospitalization: 60.2% (95% CI: 53.4-66.0); VE vs medically attended: 33.1% (30.2-35.9). Median follow-up 63 days.	11
Phase 3 Study (Japan)	Phase 3	Individuals $\geq$12 yrs	Single 50 µg dose	Immunogenicity (nAb vs XBB.1.5 at Day 29); Safety	nAb GMFR vs XBB.1.5: 11.28; Seroresponse rate: 86.8%. Safe and well-tolerated.	15
Korean Case-Control Study (Korea)	Observational	Patients undergoing COVID-19 testing	Single dose (standard of care)	VE vs symptomatic COVID-19	Adjusted VE: 56.8% (95% CI: 18.7-77.9%) in first 1-2 months.	8
mRNA-1273-P401 (NCT05933304)	Phase 3	Previously vaccinated adults	Investigational mRNA-1273.815	Immunogenicity	Study ongoing/results pending in snippets.	35

Immunogenicity in Humans:

Clinical trials have consistently demonstrated that Andusomeran (mRNA-1273.815) elicits robust neutralizing antibody (nAb) responses against the targeted Omicron XBB.1.5 variant.

• The Phase 2/3 study (NCT04927065) showed that a 50 µg booster dose of mRNA-1273.815 in adults resulted in a 17.5-fold increase in nAb geometric mean titers (GMTs) against XBB.1.5 at Day 29, relative to pre-booster levels.[5]
• Similarly, the Phase 3 study conducted in Japan reported strong nAb responses to a 50 µg dose of mRNA-1273.815 against Omicron XBB.1.5, with a geometric mean fold rise (GMFR) of 11.28 by Day 29 post-vaccination.[15]

Regarding cross-neutralizing activity against other circulating SARS-CoV-2 variants, the data indicate a more nuanced picture.

• The NCT04927065 study found that mRNA-1273.815 also induced nAb responses against more divergent variants such as JN.1, JN.1.23, and KP.2. However, the GMTs and fold-rises for these variants were notably lower at all timepoints (Day 29 and Day 181) compared to the responses against the vaccine-matched XBB.1.5 variant.[5]
• Moderna's press release from August 2023 highlighted preliminary clinical trial data confirming a significant boost in neutralizing antibodies against the then-circulating EG.5 and FL.1.5.1 variants. Earlier data presented to the FDA's Vaccines and Related Biological Products Advisory Committee (VRBPAC) in June 2023 also confirmed robust human immune responses across key circulating XBB strains.[28]

The reduced potency of XBB.1.5-induced antibodies against significantly drifted subsequent variants, such as those in the JN.1 lineage, is a critical observation. While the XBB.1.5-adapted vaccine effectively boosted immunity against its target and closely related XBB sublineages, the rapid and continuous evolution of SARS-CoV-2 underscores the challenge of maintaining broad protection. This "antigenic distance" necessitates ongoing surveillance and consideration of further updates to vaccine compositions to align with the currently dominant viral strains.

Clinical Efficacy (Real-World Effectiveness):

Real-world effectiveness (RWE) studies provide crucial insights into how Andusomeran performs in diverse, general populations under routine healthcare conditions.

• Large observational cohort studies conducted in the US using the HealthVerity claims database estimated the VE of mRNA-1273.815 against COVID-19 hospitalization to be between 51% (95% CI: 48–54%) and 60.2% (95% CI: 53.4-66.0%) in adults. VE against medically attended COVID-19 (including less severe outcomes) was estimated to be between 25% (95% CI: 24–27%) and 33.1% (30.2-35.9%). These studies had median follow-up periods ranging from 63 to 84 days, and noted that while VE might decline over time, it remained significant during the observation period.[8]
• Importantly, subgroup analyses from these RWE studies indicated continued protection against hospitalization in high-risk groups, including older adults ($\geq$65 years, VE ~56%) and immunocompromised individuals (VE ~46%).[9]
• A test-negative case-control study in South Korea reported an adjusted VE of 56.8% (95% CI: 18.7-77.9%) for the XBB.1.5 monovalent mRNA vaccine against symptomatic COVID-19 during the initial one to two months post-vaccination.[8]

These RWE findings are particularly valuable as they reflect the vaccine's performance in broader, more heterogeneous populations than typically enrolled in randomized controlled trials. The consistent demonstration of significant protection against severe outcomes like hospitalization, especially in vulnerable demographics, highlights the public health utility of the updated XBB.1.5 vaccine, even as the virus continues to evolve and efficacy against any symptomatic infection may be lower or wane more quickly.

Durability of Immune Response and Protection:

The NCT04927065 study provided data on the persistence of the immune response, noting that nAb titers against XBB.1.5 remained 5.2-fold above pre-booster levels at 6 months post-vaccination.5 Real-world VE studies also indicated that while protection against medically attended COVID-19 and hospitalization showed some decline over time, it remained statistically significant within the typical follow-up periods of these studies (up to approximately 4 months).8 The waning of immunity is an expected phenomenon with respiratory virus vaccines and is a key factor in considerations for periodic booster doses.

7. Safety and Tolerability Profile

The safety and tolerability of Andusomeran (mRNA-1273.815) have been evaluated in its clinical development program, and its profile is largely consistent with that established for previous iterations of Moderna's mRNA COVID-19 vaccines.

Table 3: Overview of Common Adverse Events Associated with Andusomeran (mRNA-1273.815)

Adverse Event Category	Common Solicited Local AEs	Common Solicited Systemic AEs	Source(s)
mRNA-1273.815 (50 µg)	Injection site pain, erythema (redness), swelling, axillary swelling/tenderness	Fatigue, headache, myalgia, arthralgia, chills, nausea/vomiting, fever	15

Note: Data primarily derived from the Japanese Phase 3 study comparing mRNA-1283.815 to mRNA-1273.815.[15] General XBB.1.5 vaccine adverse event profiles are also informative.[25]

Reactogenicity:

Clinical trial data, such as from the Phase 3 study in Japan, indicate that solicited adverse reactions (ARs) following administration of mRNA-1273.815 (50 µg dose) are common but predominantly mild to moderate in severity and transient in nature.15

• Solicited Local Adverse Reactions: The most frequently reported local AR is pain at the injection site. Other common local reactions include erythema (redness), swelling (induration), and axillary (underarm) swelling or tenderness.[15] In the Japanese Phase 3 study, a high proportion (95.7%) of mRNA-1273.815 recipients reported at least one solicited local AR within 7 days of vaccination.[15]
• Solicited Systemic Adverse Reactions: Common systemic ARs include fatigue, headache, myalgia (muscle pain), arthralgia (joint pain), chills, nausea/vomiting, and fever.[15] These reactions are indicative of the body's immune system responding to the vaccine. In the Japanese Phase 3 study, systemic ARs were also frequently reported, with a median duration typically lasting 3 to 4 days.[15]

The overall reactogenicity profile observed for mRNA-1273.815 aligns with the known safety characteristics of the broader mRNA-1273 vaccine platform (Spikevax) and its previous iterations.[5]

Serious Adverse Events (SAEs) and Adverse Events of Special Interest (AESIs):

• In the NCT04927065 Phase 2/3 study, which followed participants for 6 months after receiving mRNA-1273.815 as a booster, no vaccine-related deaths, Serious Adverse Events (SAEs), Medically Attended Adverse Events (MAAEs), AEs leading to study withdrawal, or protocol-defined Adverse Events of Special Interest (AESIs) were reported in the mRNA-1273.815 arm.[5]
• Similarly, the Japanese Phase 3 study reported no SAEs, severe unsolicited AEs, AEs leading to study discontinuation, or deaths in the mRNA-1273.815 group within the 28-day follow-up period post-vaccination.[15]
• Myocarditis and Pericarditis: It is well-established that mRNA COVID-19 vaccines, including Spikevax formulations, are associated with a rare risk of myocarditis (inflammation of the heart muscle) and pericarditis (inflammation of the lining surrounding the heart). These events typically occur within a few days to two weeks after vaccination and are more common in younger males. Regulatory authorities and product information for Spikevax XBB.1.5 include warnings regarding this risk.[20] While specific rates for Andusomeran are not detailed in these snippets, this known AESI remains a point of continued pharmacovigilance for all mRNA COVID-19 vaccines.

The consistency of Andusomeran's safety profile with that of earlier Spikevax versions is a significant finding, suggesting that the adaptation of the mRNA sequence to the XBB.1.5 variant did not introduce new, unexpected common safety signals. However, the known rare risks, such as myocarditis and pericarditis, associated with the mRNA vaccine platform necessitate ongoing monitoring and clear communication to healthcare providers and vaccine recipients.

8. Dosage, Administration, and Formulation

Recommended Dosage Regimen:

The dosage and administration schedule for Andusomeran (Spikevax XBB.1.5) are tailored to different age groups and, in some instances, an individual's prior COVID-19 vaccination or infection history. This reflects an approach to optimize the immune response and ensure safety across diverse populations.

• Individuals 12 Years of Age and Older: A single intramuscular injection of 0.5 mL is recommended. This dose typically contains 50 micrograms of andusomeran mRNA when using the 0.1 mg/mL dispersion.[18] This is generally administered irrespective of previous COVID-19 vaccination history, with a recommended interval of at least 2-3 months after the last previous COVID-19 vaccine dose if applicable.[18]
• Children 5 Years to <12 Years of Age: A single intramuscular injection of 0.25 mL is recommended. This dose typically contains 25 micrograms of andusomeran mRNA when using the 0.1 mg/mL dispersion.[18] Similar to the older age group, this is generally given irrespective of prior vaccination status, with an interval of at least 2-3 months from any previous COVID-19 vaccine dose.[18]
• Children 6 Months to 4 Years of Age:
• Without prior vaccination or known history of SARS-CoV-2 infection: A primary series of two intramuscular injections of 0.25 mL (25 micrograms mRNA each) is recommended, with the second dose administered 28 days after the first.[18]
• With prior vaccination (one or more doses) or known history of SARS-CoV-2 infection: A single intramuscular injection of 0.25 mL (25 micrograms mRNA) is recommended. This dose should be administered at least 3 months (for prior infection or completed primary series) or 1 month (if completing a primary series) after the most recent COVID-19 vaccine dose or infection.[18]
• Immunocompromised Individuals: Individuals aged 6 months and older with certain types of immunocompromise may receive additional doses of an age-appropriate 2023-2024 formula vaccine. The specific regimen, including the number and timing of additional doses, should be determined by a healthcare provider based on the individual's clinical circumstances and local public health guidelines, typically with an interval of at least 2 months following the last COVID-19 vaccine dose.[3]

The nuanced dosing schedules for younger children and immunocompromised individuals reflect the understanding that their immune responses can differ from those of healthy older children and adults. These tailored approaches aim to maximize protection in these specific groups.

Route of Administration:

Andusomeran is administered via intramuscular (IM) injection.1 The preferred injection site is the deltoid muscle of the upper arm for older children, adolescents, and adults. For infants and younger children, the anterolateral aspect of the thigh may be used.3

Vaccine Presentation and Storage:

• Formulation: Andusomeran is supplied as a white to off-white dispersion for injection.[1] It is formulated with the andusomeran mRNA encapsulated in SM-102 lipid nanoparticles. The vaccine does not contain preservatives.[46] For example, the Spikevax XBB.1.5 0.1 mg/mL dispersion provides 50 micrograms of mRNA per 0.5 mL dose or 25 micrograms per 0.25 mL dose.[22]
• Vial Presentations: The vaccine is typically available in multidose vials. For instance, the Spikevax XBB.1.5 0.1 mg/mL formulation is supplied in a multidose vial that can provide 5 doses of 0.5 mL each or 10 doses of 0.25 mL each.[22] Different vial cap colors or label borders may be utilized by manufacturers to help healthcare providers distinguish formulations intended for different age groups and dosage strengths, as has been common practice for COVID-19 vaccines.[17]
• Storage and Handling: Unopened vials of Andusomeran are stored frozen (e.g., -50°C to -15°C for Spikevax original [46]). Once thawed, vials can be stored at refrigerator temperatures (2°C to 8°C) for a specified period (e.g., up to 30 days prior to first use for Spikevax original [46]; Comirnaty XBB.1.5 up to 10 weeks [32]). It is critical that thawed vaccine vials are not re-frozen.[32] After the first dose is withdrawn from a multidose vial, there are specific time limits for its use, typically within a certain number of hours, and it should be held at room or refrigerated temperature as per the product monograph (e.g., within 12 hours for Spikevax original if held between 2°C to 25°C [46]). Detailed instructions regarding thawing, handling, and disposal are provided in the product-specific Summary of Product Characteristics or package insert and must be strictly adhered to by healthcare providers.[20]

9. Global Regulatory Status

Andusomeran (Spikevax XBB.1.5 / CX-038839 Omicron XBB.1.5) has achieved widespread regulatory authorization across the globe, reflecting a coordinated international response to the evolving SARS-CoV-2 pandemic by making updated vaccines available.

Table 4: Summary of Global Regulatory Authorizations for Andusomeran (CX-038839 Omicron XBB.1.5)

Regulatory Agency	Country/Region	Authorization Status (Product Name Examples)	Date of Authorization/Approval (XBB.1.5 version)	Indicated Age Groups (XBB.1.5 version)	Source(s)
FDA (Food and Drug Administration)	USA	Approved (Spikevax 2023-2024 Formula); EUA (Moderna COVID-19 Vaccine, 2023-2024 Formula)	September 2023	$\geq$12 years (Approval); 6 months - 11 years (EUA)	2
EMA (European Medicines Agency)	European Union	Authorized (Spikevax XBB.1.5, andusomeran)	Authorized (specific date for XBB.1.5 not in snippets, but followed earlier Spikevax approvals)	$\geq$6 months (dose varies by age and history)	3
Health Canada	Canada	Authorized (SPIKEVAX XBB.1.5, andusomeran)	September 12, 2023	$\geq$6 months	17
TGA (Therapeutic Goods Administration)	Australia	Registered (SPIKEVAX XBB.1.5, andusomeran)	October 10, 2023 (ARTG listing date)	$\geq$12 years (as per ARTG product name)	24
MHRA (Medicines and Healthcare products Regulatory Agency)	United Kingdom	Approved (Spikevax XBB.1.5, andusomeran)	September 2023	$\geq$6 months	2

Key Aspects of Authorizations:

• United States (FDA): In September 2023, the FDA granted full approval to Moderna's updated monovalent XBB.1.5 vaccine (marketed as Spikevax 2023-2024 Formula) for individuals aged 12 years and older. Concurrently, it was made available under Emergency Use Authorization (EUA) for children aged 6 months through 11 years.[2]
• Europe (EMA): Spikevax XBB.1.5, containing andusomeran, is authorized for use in individuals from 6 months of age. The dosing schedule varies, with children aged 6 months to 4 years receiving either one or two doses depending on prior vaccination or infection status, while a single injection is generally recommended for those aged 5 years and older, irrespective of previous COVID-19 vaccination history.[3]
• Canada (Health Canada): SPIKEVAX XBB.1.5 (andusomeran) received authorization on September 12, 2023, for active immunization against COVID-19 in individuals aged 6 months and older.[17]
• Australia (TGA): The SPIKEVAX XBB.1.5 (andusomeran) COVID-19 VACCINE (0.1 mg/mL suspension for injection vial - single-dose) was listed on the Australian Register of Therapeutic Goods (ARTG) on October 10, 2023. The product name on the ARTG entry specifies an indication for individuals 12 years of age and older.[24]
• United Kingdom (MHRA): The MHRA granted approval for the Moderna (Spikevax) XBB.1.5 vaccine in September 2023, for use in adults and children from 6 months of age.[2]

The largely contemporaneous regulatory authorizations of XBB.1.5-adapted vaccines by these prominent international agencies highlight a global alignment in public health strategy to address the SARS-CoV-2 pandemic. While the specific regulatory pathways (e.g., full approval versus emergency or conditional authorization) and precise age indications might exhibit minor variations due to national policies, differing data submission timelines, or regional epidemiological considerations, the overarching trend was towards making these updated vaccines rapidly accessible. This coordinated international response has been a defining feature of the global effort to manage and mitigate the impact of COVID-19.

10. Comparative Context

Direct head-to-head clinical trials comparing Andusomeran (Moderna XBB.1.5) with other XBB.1.5-adapted vaccines from different manufacturers are generally limited. However, some comparative insights can be gleaned from network meta-analyses and studies evaluating different vaccine platforms against the same variant.

A systematic review and feasibility assessment for a network meta-analysis (NMA) of Omicron-adapted COVID-19 vaccines identified 16 studies focusing on XBB formulations. Among these, eight studies, all involving mRNA formulations, were included in the NMAs, collectively representing data from 29.9 million participants. This NMA indicated that BNT162b2 (Pfizer-BioNTech) had the most extensive evidence base. Importantly, comparisons between the XBB.1.5-adapted BNT162b2 (Comirnaty) and mRNA-1273 (Spikevax, the platform for Andusomeran) suggested that both mRNA vaccines are effective and generally comparable in protecting against XBB-related hospitalizations, infections, and medically attended visits in adults. A potential, though not definitively conclusive, finding was that among elderly individuals, the estimated effectiveness against XBB-related hospitalizations numerically favored BNT162b2. However, the authors of the NMA acknowledged limitations, including assumptions made regarding effect modifiers and the sparseness of some evidence networks, which call for caution in interpreting subtle differences.[47] Such analyses, while not a substitute for direct comparative trials, offer valuable perspectives for public health decision-making by synthesizing available evidence.

Another study provided data on the Novavax COVID-19 vaccine, NVX-CoV2601, which is a recombinant spike protein subunit vaccine adjuvanted with Matrix-M. A Phase 2/3 trial (2019nCoV-313) evaluated the XBB.1.5 formulation of NVX-CoV2601 as a heterologous booster in adults who had previously received at least three doses of an mRNA COVID-19 vaccine. The results demonstrated that NVX-CoV2601 elicited superior neutralizing antibody (nAb) responses against the XBB.1.5 variant when compared to a historical comparator group that had received the prototype (ancestral strain) NVX-CoV2373 vaccine. Specifically, the baseline-adjusted nAb GMT for NVX-CoV2601 against XBB.1.5 was 905.9, whereas for NVX-CoV2373 it was 156.6, yielding a GMT ratio of 5.8 (95% CI 4.9-6.9).[48] While this study underscores the strong immunogenicity of the Novavax XBB.1.5 protein subunit vaccine, it does not offer a direct comparison with Andusomeran within the same clinical trial.

The development and authorization of multiple vaccine platforms (mRNA and protein subunit) adapted to the XBB.1.5 variant provided a diversified toolkit for public health immunization programs. While direct, large-scale randomized trials comparing these different XBB.1.5 vaccines head-to-head are generally lacking, the available immunogenicity data and real-world effectiveness studies suggest that various technological approaches can successfully yield effective variant-specific immune responses. The observed general comparability between the two XBB.1.5 mRNA vaccines from Moderna and Pfizer-BioNTech in NMAs [47], alongside strong immunogenicity data from the Novavax protein subunit vaccine [48], supports the utility of the range of updated vaccines that became available.

11. Conclusion and Future Perspectives

Andusomeran (CX-038839 Omicron XBB.1.5 / Spikevax XBB.1.5), Moderna's monovalent mRNA vaccine, emerged as a significant component of the global COVID-19 vaccination strategy, specifically engineered to offer updated protection against the previously dominant SARS-CoV-2 Omicron XBB.1.5 subvariant.[1] The vaccine's development leveraged the agility of mRNA technology, allowing for relatively rapid adaptation from earlier formulations to address the evolving viral landscape.[1] Clinical data and real-world evidence have substantiated its capacity to induce robust neutralizing antibody responses against the XBB.1.5 strain and have demonstrated meaningful effectiveness in reducing COVID-19-related hospitalizations and medically attended illnesses, particularly in vulnerable populations.[5] The safety profile of Andusomeran has remained consistent with the established profile of prior Moderna mRNA COVID-19 vaccines, primarily characterized by transient local and systemic reactogenic events.[5]

The widespread regulatory authorizations granted to Andusomeran across diverse age groups globally underscore its recognized public health value.[2] However, the relentless evolution of SARS-CoV-2, exemplified by the subsequent emergence and global spread of variants such as JN.1 and its descendants (e.g., KP.2, KP.3, LA.2), continues to pose a formidable challenge.[4] Immunogenicity data from both preclinical and clinical studies indicate that while XBB.1.5-adapted vaccines like Andusomeran effectively neutralize XBB lineage viruses, their cross-neutralizing capability against significantly drifted later variants (e.g., JN.1) is diminished.[5] This "antigenic chase," where vaccine formulations are updated to match the latest dominant variant, highlights a potential limitation in achieving sustained, broadly protective immunity against a rapidly diversifying virus.

The experience with Andusomeran and other variant-adapted vaccines signifies a maturing phase in the global pandemic response, demonstrating that vaccine technology can indeed be adapted with considerable speed. Nonetheless, the strategy of sequential monovalent vaccine updates, while effective against the targeted variant, may face challenges in providing proactive, durable protection against future, antigenically novel variants. This ongoing dynamic underscores the critical importance of continued global genomic surveillance of SARS-CoV-2 and sustained investment in next-generation vaccine research. Future efforts are likely to focus on developing vaccines that can elicit broader and more durable immune responses, potentially by targeting more conserved regions of the virus or by employing novel platforms and adjuvanting strategies designed to induce a wider spectrum of cross-protective immunity against a range of sarbecoviruses or future SARS-CoV-2 variants. The development and deployment of Andusomeran thus serve as both a testament to the achievements of modern vaccine science and a reminder of the persistent challenges posed by highly mutable respiratory pathogens.

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Disclaimer: This report is based on the provided research snippets and publicly available information as of the dates indicated in the sources. Medical and scientific information is constantly evolving.

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