The U.S. Food and Drug Administration has approved the country’s first flu vaccine that uses mRNA technology, giving Moderna the green light to offer a new option ahead of this fall’s flu season. The vaccine, called mFlusiva, is approved for adults ages 50 to 64, while adults 65 and older can receive it under accelerated approval as Moderna completes another clinical study for that age group.
The approval follows a late-stage clinical trial involving more than 40,000 older adults across 11 countries, including the United States. According to Moderna, the vaccine was about 27% more effective than a standard flu shot at preventing influenza. Researchers also reported no major safety concerns during the study. People who received mFlusiva experienced side effects such as arm pain, fatigue, headaches, and fever more often than those who got traditional flu shots, but those reactions were generally mild to moderate.
Unlike traditional flu vaccines, mRNA vaccines can be produced much more quickly. Moderna said it can manufacture mFlusiva in about two to three months after selecting the flu strain, compared with roughly six months for conventional vaccines. Scientists have long argued that faster production could make it easier to match vaccines to the flu strains that are circulating each season.
Dr. Ofer Levy, director of the Precision Vaccines Program at Boston Children’s Hospital, said choosing a flu strain six months before the season begins limits how accurately vaccines can target the virus. He also pointed out that current flu shots vary in effectiveness from year to year, with estimates ranging from 22% to 56%.
Even with the positive trial results, the vaccine’s approval faced uncertainty earlier this year. Health and Human Services Secretary Robert F. Kennedy Jr. has publicly criticized mRNA technology and has called for greater scientific scrutiny of mRNA products. Last year, the department canceled nearly $500 million in funding for mRNA vaccine research.
The FDA also briefly declined to review Moderna’s application before reversing its decision a week later. Agency officials said they wanted more data because the company had compared its vaccine with a standard flu shot in adults 65 and older, even though the Centers for Disease Control and Prevention recommends a high-dose vaccine for that age group. Moderna said the FDA had previously agreed to the trial design.
In June, the FDA’s independent vaccine advisory committee unanimously recommended approval of mFlusiva. Moderna plans to continue studying the vaccine in additional age groups as well.
The vaccine may still face challenges before becoming widely available. Flu vaccines are normally recommended by the CDC’s Advisory Committee on Immunization Practices before they are routinely used, but a federal judge has blocked the committee from meeting. Levy said doctors could still legally prescribe mFlusiva without the committee’s recommendation, though insurance coverage would likely be limited because many private insurers and federal programs rely on those recommendations when deciding which vaccines to cover.
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