The following is a summary of “Intranasal M2SR (M2-Deficient Single Replication) H3N2 Influenza Vaccine Provides Enhanced Mucosal and Serum Antibodies in Adults,” published in the January 2023 issue of Infectious Diseases by Eiden, et al.

Researchers previously showed that an intranasal dose of 108 50% tissue culture infectious dose (TCID50) M2-deficient single replication (M2SR) influenza vaccine protected against a challenge with highly drifted H3N2 influenza in a subset of subjects who showed ≥2-fold increase in microneutralization (MN) antibodies to Belgium2015 (the challenge strain) after vaccination. For a study, they presented a phase 1b observer-blinded dose-escalation research showing an enhanced proportion of responders with the immune protection signal.

108-109 TCID50 of M2SR or a placebo were given in two doses over the course of 28 days to serosusceptible participants ages 18 to 49. Prior to and following each dosage, clinical samples were taken. Getting proof that M2SR vaccinations are safe was the main goal.

All doses of the vaccination were well tolerated. Following a single 108 TCID50 M2SR dosage, 40% of participants (95% CI, 24.9%-56.7%) and 80.6% of subjects (95% CI, 61.4%-92.3%) showed ≥2-fold increases in MN antibodies against Belgium2015 (P< .001). In 71% (95% CI, 52.0%-85.8%) of recipients, a single 109 TCID50 dose of M2SR led to a ≥4-fold increase in hemagglutination inhibition antibody seroconversion against the vaccine strain. Immune responses in the mucosa and cells were also produced.

The findings suggested that M2SR may offer significant defense against infection by highly drifted H3N2 influenza viruses.