FDA clears Moderna's mRNA-based seasonal flu shot

After a series of regulatory twists and turns, the FDA has approved Moderna's mRNA-based influenza vaccine mFlusiva for adults aged 50 and over, with a launch due ahead of the coming flu season.

Prospects for the new flu shot looked decidedly rocky earlier this year, when the FDA's Center for Biologics Evaluation and Research (CBER) refused to accept Moderna's marketing application for mFlusiva – fuelled by a priority review voucher – in a letter signed by now-departed CBER head Vinay Prasad.

The refuse-to-file (RTF) letter was greeted with dismay by vaccine developers, amid fears that it was a symptom of an increasingly hostile environment at the FDA and HHS for new vaccines, particularly those based on mRNA, under the leadership of HHS Secretary Robert F Kennedy Jr, who is well known for vaccine scepticism.

The FDA claimed Moderna should have used a higher dose of the comparator vaccine used as a control in its study of mFlusiva, but Moderna hit back, accusing the regulator of deviating from already agreed-upon parameters for the filing.

Despite pushback on that interpretation of events from then FDA Commissioner Marty Makary – now also departed – the agency relented a couple of weeks later and accepted the application, reportedly under pressure from the White House.

A unanimous vote by the FDA advisory committee in favour of mFlusiva in June, despite FDA reviewers pointing to some gaps in the efficacy data submitted by the company, eased some of the nervousness about the chances of a fair review by the regulator.

Now, the approval may inject some hope into the beleaguered vaccine sector in the US, which has seen recommendations for some of the most common and widely used vaccines scaled back under Kennedy and federal funding slashed for R&D projects – particularly those based on mRNA.

A big advantage of mRNA vaccines is that they can be produced more quickly than conventional vaccines, which means developers can wait longer to see which flu strains are likely to be circulating in the next season.

mFlusiva is the first mRNA-based flu vaccine to be cleared for use in the US and Moderna's fourth FDA-approved vaccine, after its two COVID-19 products SpikeVax and mNexspike and respiratory syncytial virus (RSV) jab mResvia.

A fifth product, the combined flu/COVID-19 vaccine mCombriax, has also been approved in Europe, although the company suffered a setback to its growth plans when experimental norovirus vaccine mRNA-1403 failed a phase 3 trial.

mFlusiva has been granted full approval in adults aged 50 to 64 and accelerated approval in the over 65s, and Moderna has agreed to run a confirmatory trial in the latter age group.

The vaccine is expected to be available commercially in the US within the next few weeks, in time for the 2026-2027 flu season, although it may have missed the procurement window for some health systems. It and has also been submitted for approval in the EU, Canada, and Australia.