First mRNA Flu Shot Shows 26.6% Efficacy Boost for Adults 50+

As clinicians prepare for the upcoming flu season, the FDA's green light for Moderna's mFlusiva adds a new weapon for the 50+ demographic that may outperform traditional vaccines by a quarter. The 26.6% efficacy advantage could reshape formulary decisions and patient counseling, but the reliance on accelerated approval for the 65+ cohort leaves unanswered questions about real-world effectiveness in the highest-risk group.

In a landmark decision that could reshape the $7 billion global influenza vaccine market, the U.S. Food and Drug Administration on August 5, 2026, approved Moderna's mRNA-1010 (branded mFlusiva) as the first messenger RNA-based seasonal flu vaccine, authorized for all adults ages 50 and older. The approval harnesses the same platform that delivered COVID-19 vaccines and introduces a novel mechanism against a pathogen responsible for up to 650,000 deaths worldwide annually. Older adults bear the heaviest burden—accounting for the vast majority of influenza-related hospitalizations and deaths—making the targeted approval age group especially significant.

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Serious adverse event rates were 2.2% for mRNA-1010 versus 1.9% for standard-dose vaccines.

The pivotal data came from the phase III Fluent trial, a randomized, observer-blinded study that enrolled over 40,000 participants during the 2024–2025 Northern Hemisphere season. Those receiving mRNA-1010 demonstrated a relative vaccine efficacy of 26.6% compared with a standard-dose influenza vaccine across all participants aged 50 and older. Among the subset aged 65 and over, efficacy reached 27.4%. A separate immunogenicity study in the 65+ population showed superiority over a high-dose comparator vaccine. The FDA granted traditional approval for adults 50–64, based on clinical endpoints, while accelerated approval was given for those 65 and older, contingent on a postmarketing effectiveness study to confirm real-world clinical benefit.

Safety was generally comparable: most adverse reactions were mild to moderate and transient. Serious adverse event rates were 2.2% for mRNA-1010 versus 1.9% for standard-dose vaccines. The FDA advisory committee voted unanimously to recommend approval, reflecting confidence in the benefit–risk profile.

The mRNA platform’s speed advantage is critical. Traditional egg-based influenza vaccine manufacturing takes six to nine months, forcing strain selection in February for the fall season. This often leads to substantial mismatches, with vaccine effectiveness historically ranging between 20% and 60%. mRNA manufacturing, by contrast, can conclude within weeks, allowing strain selection much closer to season onset and facilitating rapid updates should circulating strains shift. The trivalent formulation targets influenza A/H1N1, A/H3N2, and B/Victoria; a quadrivalent version could follow.

For Moderna, the approval diversifies revenue beyond its declining COVID-19 franchise. The U.S. flu vaccine market comprises approximately 150–170 million doses annually, supported by Medicare and private insurers. The 50-plus U.S. population exceeds 110 million, though vaccination rates are roughly 40% in the 50–64 group and around 70% in the 65-plus group. If mRNA-1010 captures even a modest share, it could add billions to Moderna’s top line. The decision also validates the mRNA platform for non-pandemic respiratory viruses, bolstering confidence in Moderna’s pipeline—including RSV, cytomegalovirus, and combination COVID-19/flu vaccines.