Moderna mRNA Flu Vaccine Outperforms Standard Shot in Phase 3 Trial

Moderna's mRNA-based seasonal flu vaccine demonstrated superior efficacy to a standard flu shot in an international late-stage trial involving more than 40,000 adults aged 50 and older. Researchers reported the findings Wednesday in the New England Journal of Medicine.

The shot was 26.6 percent more effective than an approved standard-dose vaccine from GSK, surpassing the study's primary goal of proving it was at least as good as existing options. The trial results come as the vaccine remains under review. A decision is expected by August 5.

If approved, it would become the first seasonal flu vaccine in the United States produced with mRNA technology, which allows faster manufacturing than traditional methods. Side effects such as injection-site pain, fatigue, headache and muscle aches occurred more frequently with the mRNA vaccine than with the standard shot.

Most reactions were mild to moderate and resolved quickly. Severe side effects were reported in 2.2 percent of participants who received the mRNA shot and 1.9 percent who received the standard dose, a balance the researchers described as comparable.

Overall safety aligned with results from earlier late-stage trials, according to the study authors. The findings were published by Dr. Isabel Leroux-Roels of Ghent University and colleagues. They concluded that the data support the vaccine's role in improving influenza prevention.

“These findings support the role of mRNA-1010 in improving influenza prevention.”

The company had initially faced a rejection of its application in February. Officials cited concerns that the trial had used a standard-dose comparator rather than a high-dose vaccine recommended for adults 65 and older in the United States. After further discussions, the agency accepted an amended application on the condition that the company conduct an additional study in older adults following approval.

Regulatory reviews for the mRNA flu vaccine are also underway in the European Union, Canada and Australia. The company secured approval in April for a combined mRNA vaccine targeting both flu and COVID-19 in Europe. The flu-only version would represent a significant expansion of mRNA technology beyond its initial use in COVID-19 vaccines.

Health Secretary Robert F. Kennedy Jr. has voiced longstanding criticism of mRNA platforms and has canceled substantial research funding tied to the technology while making statements not supported by available scientific evidence. The vaccine's path through review occurs against that backdrop of heightened scrutiny.

The trial data provide concrete evidence of improved protection against flu illness compared with conventional shots. Publication in the New England Journal of Medicine adds weight to the results as officials weigh final approval.