GeoVax's Multi-Antigen COVID-19 Vaccine Shows Promising Results in Immunocompromised Patients

GeoVax Labs (search)Search company, Inc. (Nasdaq: GOVX) has reported promising clinical results for its multi-antigen SARS-CoV-2 (search)Search disease vaccine candidate, GEO-CM04S1View drug details, demonstrating durable immune responses in both healthy volunteers and immunocompromised patients.

The clinical-stage biotechnology company presented new data at the 25th Annual World Vaccine Congress in Washington, D.C., highlighting the vaccine's performance across several Phase 1 and 2 clinical trials. The presentation, delivered by Don J. Diamond, Ph.D., showcased results from studies involving healthy adults as well as vulnerable populations including stem cell transplant recipients and patients with chronic lymphocytic leukemia (search)Search disease (CLL).

Dual-Antigen Approach Shows Broad Immunity

GEO-CM04S1View drug details is based on the synthetic Modified Vaccinia Ankara (MVA) vector platform and uniquely expresses both the Spike (search)Search target (S) and Nucleocapsid (search)Search target (N) antigens of SARS-CoV-2 (search)Search disease. This dual-antigen approach appears to generate broader and more durable immune responses compared to single-antigen vaccines.

In a Phase 1 trial with healthy adults, 100% of participants (34/34) produced Spike (search)Search target IgG antibodies, while 94% (32/34) developed Nucleocapsid (search)Search target IgG antibodies. Additionally, 98% (48/49) demonstrated T cell responses to either antigen following vaccination, with no serious safety concerns reported across varying dose levels.

Superior Performance in Immunocompromised Patients

Perhaps most notably, GEO-CM04S1View drug details showed particularly strong results in immunocompromised populations—groups that have historically responded poorly to existing mRNA vaccines.

In stem cell transplant recipients, the vaccine induced antibody titers and T cell responses that exceeded those observed in healthy volunteers. More dramatically, a randomized Phase 2 trial comparing GEO-CM04S1View drug details to the Pfizer-BioNTech (search)Search term (ComirnatyView drug details®) vaccine in CLL patients revealed significantly higher T cell response rates with GEO-CM04S1.

"At Day 56 of the study, 6 of 15 patients in the GEO-CM04S1View drug details arm achieved 3-fold increases in Spike (search)Search target or Nucleocapsid (search)Search target-specific T cells versus only 2 of 14 in the ComirnatyView drug details arm," Diamond reported. The Data and Safety Monitoring Board subsequently recommended halting enrollment in the Pfizer arm due to underperformance, while continuing enrollment in the GEO-CM04S1 arm.

Effective Booster at Lower Doses

The vaccine also demonstrated strong performance as a booster in healthy volunteers previously vaccinated with mRNA or protein-based COVID-19 (search)Search disease vaccines. In this Phase 2 booster trial, participants showed significant increases in Spike (search)Search target, RBD, and Nucleocapsid (search)Search target IgG antibody responses, as well as neutralization titers against multiple COVID-19 variants, including XBB.1.5.

Importantly, these robust responses were achieved at both higher and lower dose levels, with no meaningful differences between them—suggesting potential dose-sparing capabilities.

Potential Dual Protection Against COVID-19 and Mpox

In a separate presentation at the AAI Annual Meeting 2025, researchers highlighted GEO-CM04S1View drug details's potential to provide protection against both COVID-19 (search)Search disease and Mpox (search)Search disease. The presentation, titled "Immunogenicity of Synthetic MVA-based Vaccine COH04S1 Against SARS-CoV-2 (search)Search disease in Post-HCT/CAR-T Patients and Its Cross-Protective Potential Against Mpox," revealed that sera from COH04S1-vaccinated individuals demonstrated cross-reactive immunity against Mpox virus.

These immune responses were found comparable to those in humans receiving the currently licensed smallpox/Mpox (search)Search disease vaccine (JynneosView drug details). Furthermore, sera from vaccinated individuals protected against lung infection in susceptible mice challenged with Mpox virus.

"These findings underscore the differentiated potential of GEO-CM04S1View drug details to serve dual roles as both a next-generation multi-antigen COVID-19 (search)Search disease vaccine and a cross-protective agent against Mpox (search)Search disease," said Kelly T. McKee, Jr., M.D., Chief Medical Officer of GeoVax. "The ability to stimulate strong, broad, and durable immunity, particularly in immunocompromised individuals, represents a meaningful advancement over current vaccines."

Ongoing Clinical Development

GEO-CM04S1View drug details is currently being evaluated in three Phase 2 clinical trials:

1. As a primary vaccine for immunocompromised patients such as those undergoing stem cell transplantation or CAR-T therapy, in a randomized comparison to mRNA vaccines

2. As a booster vaccine for patients with chronic lymphocytic leukemia (search)Search disease (CLL), in a randomized comparison to an mRNA vaccine

3. As a booster for healthy adults previously vaccinated with mRNA COVID-19 (search)Search disease vaccines

"The clinical performance of GEO-CM04S1View drug details across diverse and high-risk populations supports our mission to deliver broad and lasting protection through next-generation vaccines," said David A. Dodd, Chairman, President, and CEO of GeoVax. "Our data continues to demonstrate strong, durable immune responses in both healthy and immunocompromised populations—a critical feature of our vaccine for public health preparedness."

Market Implications

The positive clinical results come at a time when public health officials are emphasizing the need for more effective vaccines for vulnerable populations. Immunocompromised patients, including those with blood cancers and transplant recipients, remain at higher risk for severe COVID-19 (search)Search disease outcomes despite current vaccination options.

If GEO-CM04S1View drug details continues to demonstrate superior performance in these populations through later-stage trials, it could potentially fill an important gap in the current vaccine landscape. The added potential for cross-protection against Mpox (search)Search disease further enhances its public health value, particularly in regions where Mpox is endemic.

GeoVax holds worldwide rights for its technologies and products, positioning the company to potentially capitalize on these developments as the vaccine advances through clinical trials.