Investigational Influenza Vaccine Shows Positive Results in Human Challenge Study

FluGen, a clinical-stage vaccine company, announced its investigational influenza vaccine candidate, Bris2007 M2SR, induced neutralizing antibodies for participants in its human challenge study against H3N2 influenza strain.

“Current vaccines are strain-specific and in recent years they have had low efficacy against H3N2 influenza, especially when the vaccine is mismatched to circulating virus,” Robert Belshe, MD, the Diana and J. Joseph Adorjan endowed professor of Infectious Diseases and Immunology, Emeritus, at Saint Louis University, and Chair of the FluGen Clinical Advisory Board, said.

The human challenge trial included participants who were aged 18-55 years that were randomized to receive a single intranasal spray, either with placebo or with a 108 TCID50 dose of monovalent H3N2 M2SR vaccine. Four weeks later, they were challenged with an influenza strain 7 years drifted from the vaccine, a period during which WHO recommended four H3N2 vaccine strain changes to maintain match against seasonal influenza virus.

Interested in learning more about human challenge trials? Read more about the bioethics of such trials and what considerations go into them before commencing. 

The challenge study results demonstrated that, despite the significant mismatch of vaccine and challenge strains, a single dose of Bris2007 M2SR induced neutralizing antibody to the vaccine (48% of recipients) and challenge strain (27% of recipients).

Overall, 54% of M2SR subjects were infected after challenge, compared to 71% of placebo subjects. The subset of M2SR subjects with a vaccine-induced microneutralization response against the challenge virus had reduced rates of infection after challenge (38% vs. 71% of placebo subjects, P=0.0505) and reduced illness.

In terms of adverse events, they were considered mild and similar in frequency between placebo and M2SR recipients. Most treatment emergent adverse events were mild in severity, and no vaccine virus shedding was detected in any of the subjects. The correlation between serum markers and efficacy in the trial is expected to accelerate further development of M2SR.

The M2SR platform is a supra-seasonal, live, single-replication, intranasal flu vaccine. M2SR stimulates mucosal, humoral, and cellular immunity.

“The M2SR vaccine candidate is designed to induce a broad, multi-effector immune response, and this study demonstrated that subjects with vaccine-induced neutralizing antibodies were protected against infection and illness following challenge with an antigenically drifted virus,” Belshe said. “Inactivated vaccines have not had that broad protection. This is the first demonstration in adults of vaccine-induced protection against a highly drifted H3N2 challenge virus.”