Researchers reported that a Moderna mRNA-based seasonal flu vaccine worked better than conventional flu shots in a late-stage, phase 3 international clinical trial of more than 40,000 adults aged ⁠50 and older.

This is great news, since the currently available flu vaccine has only a moderate effectiveness. The study also stated that the benefits of an mRNA vaccine, including the capacity for rapid updates, as demonstrated for the rapidly evolving COVID variants, compared to the current time-consuming egg-based development and production for most licensed flu vaccines.

This article will review the new data for effectiveness and safety from the mRNA flu vaccine clinical trial.

Moderna mRNA flu vaccine trial results

In a paper published on 7 May 2026 in the New England Journal of Medicine, Isabel Leroux-Roels, Ghent University, Belgium, and colleagues examined the results from a phase III trial that randomly assigned 40,703 adults 50 and older (mean age 64, 57% women) to receive Moderna’s trivalent mRNA-1010 flu vaccine (37.5 μg, which includes 12.5 μg each of A/H1N1, A/H3N2, and B/Victoria) or a licensed standard-dose trivalent or quadrivalent flu vaccine comparator.

Flu illness in both groups was confirmed by reverse transcriptase-polymerase chain reaction testing.

Here are the key results:

• Influenza A or B illness was observed in 2% of participants who received the trivalent mRNA-1010 vaccine, compared with 2.8% of those who received approved standard-dose vaccines through the end of the flu season. The mRNA-1010 vaccine had a higher relative vaccine effectiveness of 26.6% compared to the standard flu vaccines. (Note: relative vaccine effectiveness is the difference in effectiveness between the mRNA-1010 vaccine and the standard, currently available vaccines. Thus, the mRNA-1010 is 26.6% more effective than the standard vaccines.)
• Among the more than 19,000 adults ages 65 and older in the clinical trial, a population more susceptible to flu complications, the relative vaccine effectiveness of mRNA-1010 was 27.4% compared to the standard flu vaccines.
• Medically-attended influenza-associated outcomes across all healthcare settings occurred in 80 participants in the mRNA-1010 group and 120 in the standard-dose comparator group, which corresponded to a relative vaccine effectiveness of 33.7%.
• Among the 64 participants who sought higher-level care, hospitalization, emergency department, or urgent care encounters occurred in 22 recipients of mRNA-1010 and 42 recipients of the standard-dose comparator, which indicated a relative vaccine effectiveness of 47.9%.
• The mRNA-1010 vaccine candidate had a substantially higher risk of solicited adverse events compared with standard vaccines, including injection-site pain (65.8% vs 29.8%), fatigue (45.1% vs 20.3%), headache (37.8% vs 18.0%), and myalgia (35.4% vs 11.6%). Most reactions were mild to moderate and transient. Serious adverse events were “infrequent and similar in the two groups.”
• Overall, 2.2% of mRNA-1010 recipients had adverse events (only three were considered vaccine-related) versus 1.9% in the comparator group (only two were vaccine-related).

The authors concluded:

The consistency of relative vaccine efficacy across these many outcomes suggests that mRNA-1010 efficacy is broadly applicable across diverse populations and the spectrum of influenza disease.

Summary

This clinical trial showed that the Moderna mRNA flu vaccine candidate had a substantially higher effectiveness and similar adverse effects compared to the currently available flu vaccines.

Earlier this year, the FDA refused to review Moderna’s application for the vaccine, although they quickly reversed that decision. However, with the antipathy against mRNA vaccines across the Department of Health and Human Services, I worry that this vaccine will not get approval.

Since seniors are more susceptible to serious flu complications, they need a more effective flu vaccine than the current ones. But I’m not sure that it will matter to the anti-vaccine crowd, especially the ones in government.

Let’s hope that this vaccine gets approval.

Citations

• Leroux-Roels I, Huang G, Ferguson M, Kohli A, Clark R, Bickel M, Soens M, Du E, Pucci A, Hicks B, Eschen C, Das R, Wilson E; Fluent Trial Investigators. Efficacy and Safety of an mRNA Seasonal Influenza Vaccine in Adults. N Engl J Med. 2026 May 7;394(18):1803-1813. doi: 10.1056/NEJMoa2516491. PMID: 42090792.

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