A Phase 2a, Randomized, Observer-Blind, Placebo Controlled, Dose-Confirmation Study to Evaluate the Safety, Reactogenicity, and Immunogenicity of mRNA-1273 SARS-COV-2 Vaccine in Adults Aged 18 Years and Older

Number of Participants With Solicited Local and Systemic Adverse Reactions (ARs)

Time Frame: 7 days post-vaccination

Solicited ARs, including local and systemic ARs were collected in the eDiary. Local ARs included: pain at injection site, erythema (redness) at injection site, swelling/induration (hardness) at injection site, and localized axillary swelling or tenderness ipsilateral to the injection arm. Systemic ARs included: headache, fatigue, myalgia (muscle aches all over the body), arthralgia (aching in several joints), nausea/vomiting, rash, body temperature (potentially fever), and chills. All solicited ARs (local and systemic) considered causally related to injection. ARs were graded 0-4 as reviewed and confirmed by Investigator; lower score indicates lower severity and a higher score indicates greater severity. Note, not all solicited ARs were considered adverse events (AEs). The Investigator reviewed whether the solicited AR was also to be recorded as an AE. A summary of SAEs and all nonserious AEs ("Other"), regardless of causality, is located in the Reported "Adverse Events" section.

Number of Participants With Unsolicited AEs

Time Frame: Up to 28 days post-vaccination

An AE was defined as any untoward medical occurrence associated with the use of a drug in humans, whether or not considered drug related. A treatment-emergent AE (TEAE) was defined as any event not present before exposure to vaccine or any event already present that worsens in intensity or frequency after exposure. Any abnormal laboratory test result (hematology, clinical chemistry, or prothrombin time \[PT\]/partial thromboplastin time \[PTT\]) or other safety assessment (for example, electrocardiogram, radiological scan, vital sign measurement), including one that worsens from baseline and is considered clinically significant in the medical and scientific judgment of the Investigator. A summary of SAEs and all nonserious AEs ("Other") reported up to the end of the study (up to Month 15), regardless of causality, is located in the Reported "Adverse Events" section.

Number of Participants With Medically-Attended Adverse Events (MAAEs)

Time Frame: Up to Month 15

An MAAE is an AE that leads to an unscheduled visit to a healthcare practitioner (HCP). A summary of SAEs and all nonserious AEs ("Other"), regardless of causality, is located in the Reported "Adverse Events" section.

Number of Participants With SAEs

Time Frame: Up to Month 15

An SAE was defined as any AE that resulted in death, is life-threatening, required inpatient hospitalization or prolongation of existing hospitalization, resulted in disability/permanent damage, was a congenital anomaly/birth defect, or was an important medical event. A summary of SAEs and all nonserious AEs ("Other"), regardless of causality, is located in the Reported "Adverse Events" section.

Part A: Level of Severe Acute Respiratory Syndrome Coronavirus (SARS-COV-2)-Specific Binding Antibody (bAb) as Measured by Enzyme-Linked Immunosorbent Assay (ELISA)

Time Frame: Days 1 (Baseline), 29, 43, 57, and 209

The geometric mean (GM) level of VAC58 spike immunoglobulin G (IgG) antibodies, as measured by ELISA specific to the SARS-CoV-2 spike protein is reported. Antibody values reported as below the lower limit of quantification (LLOQ) were replaced by 0.5\*LLOQ. Values that were greater than the upper limit of quantification (ULOQ) were converted to the ULOQ if actual values were not available. LLOQ was 1 and ULOQ was 2052. The 95% confidence intervals (CIs) were calculated based on the t-distribution of the log-transformed values or the difference in the log-transformed values for GM value, respectively, then back transformed to the original scale for presentation.

Part B: Level of SARS-CoV-2-Specific bAb as Measured by ELISA

Time Frame: Days 1 (Baseline) and 29

The GM level of VAC65 spike IgG antibodies, as measured by ELISA specific to the SARS-CoV-2 spike protein is reported. Antibody values reported as below the LLOQ were replaced by 0.5\*LLOQ. Values that were greater than the ULOQ are converted to the ULOQ. LLOQ was 1 and ULOQ was 2052. The 95% CIs were calculated based on the t-distribution of the log-transformed values or the difference in the log-transformed values for GM value, respectively, then back transformed to the original scale for presentation. The PP Set included participants with a study injection, required baseline data, had postinjection results at timepoint of primary interest for immunogenicity analysis, no major protocol deviations impacting immune response, and didn't have SARS-CoV-2.

Part C: Level of SARS-CoV-2-Specific bAb as Measured by MSD

Time Frame: Days 1 (Baseline), 8, 15, and 29

The GM level of SARS-CoV-2 protein antibody against B.1.351, as measured by MSD MULTIPLEX is reported. Antibody values reported as below the LLOQ were replaced by 0.5\*LLOQ. Values that were greater than the ULOQ are converted to the ULOQ. LLOQ was 18 and ULOQ was 4200000. The 95% CIs were calculated based on the t-distribution of the log-transformed values or the difference in the log-transformed values for GM value, respectively, then back transformed to the original scale for presentation.