Safety and immunogenicity of an investigational mRNA-lipid nanoparticle-based monovalent influenza vaccine: Results from a phase 1, randomized, dose-escalation study.

In 30 seconds

This randomized, controlled, phase 1 dose-escalation study assessed safety and immune responses to a monovalent mRNA-lipid nanoparticle influenza A/H1N1 vaccine in younger adults aged 18–45 years and older adults aged 60–80 years, compared with a licensed quadrivalent vaccine. Solicited adverse-event rates generally rose with mRNA dose, but no safety concerns were identified. By day 22, adjusted geometric mean increases in H1N1 hemagglutination-inhibition titers ranged from 6.2 to 36.7 across groups; responses were dose-dependent and higher than with the comparator at mRNA doses above 1 µg.

Key findings

• Solicited adverse events occurred in 62.5%–100% of younger mRNA-vaccine recipients across dose groups, versus 88.6% with the licensed vaccine; no safety concerns were identified.
• At day 22, adjusted geometric mean increases in H1N1 hemagglutination-inhibition titers ranged from 6.2 to 36.7 and increased with mRNA dose.
• At day 183, titers had declined but remained above baseline, with geometric mean increases of 2.9–14.0.
• The mRNA vaccine elicited numerically higher hemagglutinin-specific CD4+ T-cell responses, predominantly Th1, than the licensed vaccine in both age groups.

Why it matters

The findings provide early human evidence that an mRNA influenza vaccine can induce antibody and cellular responses in younger and older adults, while identifying dose-related reactogenicity for further evaluation. The persistence of antibody titers above baseline at day 183 supports continued study, but these immune outcomes do not establish protection against influenza illness.

What to keep in mind

This was a phase 1 study of a monovalent candidate, with follow-up reported to day 183; it assessed immune responses rather than clinical protection against influenza.