The US Food and Drug Administration (FDA) has approved the first influenza vaccine built on messenger RNA technology, clearing the way for Moderna to sell the shot to older Americans this winter.
The agency signed off on the product, branded mFlusiva, on August 5 for adults aged 50 and over. Adults aged 50 to 64 were granted a full licence while those aged 65 and over were covered by accelerated approval, with a further trial required.
Reviewers logged 23 deaths of unspecified cause among recipients against nine on comparator shots, according to the FDA briefing document. The gap widened to 29 against 12 once sudden deaths were pooled and no autopsies were carried out on the Moderna group.
The agency concluded the imbalance was unlikely to be caused by the vaccine, citing pre-existing illness and no clustering after injection. Overall mortality was level at 0.3 per cent in both arms.
Approval rested on a trial of 40,805 adults across 11 countries over a single flu season. The vaccine cut laboratory-confirmed influenza cases by 26.6 per cent compared with a standard-dose shot.
Reported reactions were markedly more common than with the comparator. Local reactions affected 67.5 per cent of recipients against 32.1 per cent, and systemic reactions 58 per cent against 32.4 per cent.
Severe systemic reactions were reported by 5.5 per cent of recipients compared with 0.9 per cent on the older vaccine. Reviewers put the median duration at about two days and judged the profile acceptable.
They separately noted that the antibody tests underpinning the over-65 approval used laboratory-grown virus matched to the Moderna product, a choice they said could systematically favour it over egg-based rivals.
Protection was also weaker among participants with existing health problems, at 22.3 per cent against 32.1 per cent in healthier volunteers. The trial excluded immunocompromised people and enrolled few frail older adults.
Moderna chief executive Stéphane Bancel said flu “remains a significant public health challenge”.
In February the FDA’s then head of biologics, Vinay Prasad, refused to review the file over the trial design, a decision reversed two weeks later.
Prasad left the agency at the end of April and an advisory committee backed the vaccine unanimously in June. Health and Human Services Secretary Robert F Kennedy Jr has repeatedly questioned the technology and a department spokesman said mRNA products “warrant heightened scientific scrutiny”.
In the European Union the shot remains under assessment by the European Medicines Agency. The European Commission has already authorised mCombriax, a combined flu and Covid-19 vaccine using the same influenza component, for adults aged 50 and over across the bloc.
