FDA approves the first mRNA flu shot after refusing to review it

The Food and Drug Administration has approved the first flu vaccine made with mRNA, the technology behind the covid shots. Moderna's mFLUSIVA is cleared for adults aged 50 and over and the company expects it to be available for the coming flu season.

The approval is a first for influenza, and it arrives by an unusual route. Earlier this year the same agency refused even to review Moderna's application, then reversed itself about a week later after the company changed what it was asking for.

It also lands inside a health department whose secretary, Robert F. Kennedy Jr., has criticised mRNA technology repeatedly and last year cancelled 22 vaccine development projects that use it. The FDA sits within his department.

What the trial found

The evidence comes from a trial of about 40,000 people. It compared mFLUSIVA against a standard dose flu vaccine in adults aged 50 and over, and found the mRNA shot performed better. STAT reported a figure of about 27 percent for adults aged 50 to 64, and Moderna's own trial results give a relative efficacy of 26.6 percent overall.

Relative efficacy is a comparison, not an absolute. A figure of 26.6 percent does not mean the vaccine prevents a quarter of flu cases. It means that among people who got the mRNA shot there were about a quarter fewer cases than among those who got the standard dose vaccine it was tested against.

In adults 65 and over Moderna reports 27.4 percent. That group is where flu does most of its damage, and it is also where the approval is conditional rather than final.

The split decision

The agency granted standard approval for adults aged 50 to 64 and accelerated approval for those 65 and over. Accelerated approval is a faster clearance that comes with a debt: the company has to run a further study, and the clearance can be withdrawn if the results do not hold up.

Moderna has agreed to run one. STAT reported it will be a trial after licensing that compares the shot against the high dose and adjuvanted vaccines older patients are usually steered to, which is the comparison the agency complained was missing the first time round.

The split traces directly to the fight over the application. When the FDA first refused to file it, the agency's then head of biologics, Dr. Vinay Prasad, faulted the trial for not comparing the new shot against a vaccine specifically recommended for people 65 and over. Prasad left the FDA at the end of April, months before this approval.

Moderna's answer was to ask for less. It revised the application to seek full approval only for the 50 to 64 group, accelerated approval above that, and volunteered the extra study. The agency said discussions had produced a revised regulatory approach and an amended application, which it accepted.

the ongoing potential of our mRNA platform to help address important public health challenges through continued scientific innovation

Why mRNA matters for flu

Most flu vaccines are still grown in chicken eggs, a process that takes months, though some supply is now cell based. Each year a World Health Organization committee picks the strains months in advance, manufacturers commit to that choice, and when the strains shift the season's vaccine works less well.

mRNA does not need eggs and can be reprogrammed quickly, which is the argument for it here. It shortens the gap between choosing a strain and shipping doses, and that gap is where much of the mismatch between vaccine and virus is created.

Dr. Céline Gounder, a CBS News medical correspondent and editor at large for public health at KFF Health News, put the speed difference in terms of a pandemic. With egg based technology, she said, producing enough vaccine for a new pandemic strain to cover a quarter of the world's population would take 18 months.

With an mRNA vaccine, you could do it much more quickly.

That is the case for the platform rather than for this particular shot. Nothing in the approval says the mRNA vaccine will be updated faster in practice, only that the technology allows it.

Reported side effects are the familiar ones. Gounder listed pain at the injection site, fatigue and headache, and STAT reported substantially more side effects in the mRNA arm of the trial than in the comparator, mostly mild and lasting a day or two. Anyone weighing the shot should ask a clinician rather than a news article.

The politics around it

The approval is awkward for the department that issued it. Kennedy has questioned mRNA technology repeatedly, and last year his department cancelled 22 mRNA vaccine development projects. The FDA nonetheless cleared an mRNA product on the evidence in front of it.

Whether that reflects independence or simply the limits of what a secretary controls is not clear from the record. Approval decisions sit with FDA reviewers, but the department sets which research gets funded, and those are different levers.

What is clear is that the objection that shaped this approval came from inside the agency rather than from the secretary's office, and that it was about the evidence in the oldest patients rather than about mRNA itself. An FDA advisory panel voted unanimously in June to back the vaccine.

What it means at the pharmacy counter

For most people the practical effect this autumn is one more option. Moderna expects the shot to be available for the 2026 to 2027 season, alongside the egg based vaccines that have been used for decades.

Anyone under 50 is not covered by this approval and will be offered the existing vaccines. Anyone over 65 will be offered a shot whose clearance in their age group is provisional and rests on a study that has not finished.

An approval is not a recommendation. It establishes that a vaccine may be sold, not who should prefer it, and the guidance about which shot a given patient ought to get is settled separately from the approval issued on August 5.

The test that has not happened yet

The bigger test is one the trial cannot answer yet. If mRNA lets manufacturers pick strains later and still ship on time, the benefit shows up in seasons when the strain selection would otherwise have missed. That will take several flu seasons to demonstrate, and the postmarketing study runs across two of them.

Nothing here is medical advice. The approval, the trial figures and the conditions attached to them are all in the FDA's decision and Moderna's published results, and anyone weighing the shot should take the question to a clinician.