FDA approves Moderna's mRNA flu vaccine after initially refusing to review it

The mFlusiva vaccine will soon be available for adults aged 50 and over.

After initially refusing to even review it, the US Food and Drug Administration (FDA) has approved Moderna's mRNA seasonal flu vaccine, the pharmaceutical company announced in a press release . Known as mFlusiva (or mRNA-1010), the immunization is effective against the four most common strains of influenza and has been in human testing trials since 2021 . Those variants cause up to five million severe flu cases every year and result in as many as 650,000 respiratory deaths annually, the World Health Organization (WHO) wrote in 2017 .

The vaccine is approved for adults aged 50 and over. Moderna said it received approval for people between the ages of 50 to 64 after a Phase 3 clinical trial that enrolled 40,805 adults across 11 countries. It also received accelerated approval for patients 65 and older. The trial's objectives were to evaluate the safety of the mFlusiva and its relative efficacy compared to an approved and effective non-mRNA vaccine (comparator).

In its study , Moderna's researchers concluded that "mRNA-1010 was superior to standard-dose licensed vaccines for prevention of... influenza-like illness in adults 50 years of age or older." However, it added that "solicited adverse events" were more frequent with mRNA-1010 than current flu vaccines, including injection-site pain, fatigue, headache and myalgia (muscle pain). Most adverse reactions were "mild to moderate and transient," the study states.

Approval for Moderna's flu vaccine got off to a rocky start after the FDA refused to even review Moderna's application. The US drug regulator initially said that Moderna's comparator vaccine didn't represent the "best available standard of care" in the US at the time of the study, and that it preferred a higher-dose vaccine for older adults as a comparator.

The FDA's refusal to review the vaccine came after the director of drug approval overruled career scientists, prompting critics to call the move political. "It's all pretext and obfuscation when the real agenda is rejecting conventional science and serving a predetermined anti-vaccine agenda," law professor Richard Hughes IV told The Guardian at the time.

After less than a week, however, the FDA reversed course and agreed to review Moderna's application, likely because it previously told Moderna that its selected comparator vaccine was just fine. "We agree that it would be acceptable to use a licensed standard dose influenza vaccine as the comparator in your Phase 3 study," the FDA told the company prior to the rejection.

mRNA vaccines from Moderna and others have generally sailed through trials due to inherent properties that make them safer and more effective than standard vaccines. Those include high efficacy in preventing severe illness, rapid development times, adaptability to new strains, manufacturing without live viruses, fewer side effects for immunocompromised people, and the ability to trigger a strong immune response without the risk of altering human DNA.