The approval covers two age groups — adults 50 to 65 and adults 65 and up — but comes with strings attached. Moderna must run an additional clinical trial in the older group, the company said in a release. In a late-stage trial of more than 40,000 older adults across 11 countries, mFlusiva was about 27% more effective than a standard flu shot.
Why an mRNA Flu Shot Matters
Traditional flu vaccines are grown in chicken eggs or cell cultures, a process that takes roughly six months from the moment scientists pick which strains to target. Moderna says its mRNA platform compresses that timeline to two to three months. Faster manufacturing means public health officials can wait longer into flu season to choose strains, improving the odds that the vaccine matches what is actually circulating.
“If you’re choosing the strain half a year before, how good can we be at sharpshooting?” said Dr. Ofer Levy, director of the Precision Vaccines Program at Boston Children’s Hospital.
The flu hospitalizes hundreds of thousands of people in the U.S. every year, according to the Infectious Diseases Society of America, and kills tens of thousands. Young children and older adults are most likely to get severely ill. The traditional flu shot ranges in effectiveness from 22% to 56%, per the Mayo Clinic. “We wish it were higher, quite frankly,” Levy said.
A Politically Charged Approval
Even though mFlusiva outperformed the standard flu shot in late-stage testing, its approval was never guaranteed. Health and Human Services Secretary Robert F. Kennedy Jr. — a longtime anti-vaccine activist — has repeatedly criticized mRNA technology, calling the Covid vaccines “the deadliest vaccine ever made.” Last year, HHS under Kennedy canceled nearly $500 million in funding for mRNA vaccine research.
Asked about Kennedy’s stance on mFlusiva, an HHS spokesperson said: “Secretary Kennedy has been clear that he believes mRNA products warrant heightened scientific scrutiny. That’s why this vaccine is entering the market with some of the strongest post-market study commitments FDA has required, particularly for individuals 65 years of age and older.”
The FDA initially refused this year to review Moderna’s application before reversing course a week later. Agency officials said they wanted more data because Moderna had compared its vaccine with a standard flu shot in adults 65 and older, even though the CDC recommends a high-dose flu vaccine for that age group. Moderna has said the FDA previously signed off on the trial design. In June, the FDA’s independent vaccine advisory committee unanimously recommended approving the vaccine.
Trial Findings and Side Effects
The late-stage trial enrolled older adults across 11 countries, including the U.S. Rates of side effects — injection-site pain, fatigue, and headaches — were more common in the mFlusiva group than among those who received a standard flu shot, but were still mild to moderate. Drug makers typically start clinical trials in the highest-risk groups first, and Moderna said it plans to study the vaccine in other age groups going forward.
A combination flu and Covid vaccine from Moderna, also built on mRNA, was approved by the European Union in April. Moderna withdrew its application for U.S. approval of that combination shot last year despite positive late-stage trial results.
What Happens Next
Moderna said mFlusiva will be available for this fall’s flu season, but a major obstacle remains: the CDC’s Advisory Committee on Immunization Practices, which formally recommends vaccines for use in the U.S., has been blocked from convening by a federal judge.
Levy said mFlusiva could still be legally prescribed without ACIP’s sign-off. But without a formal recommendation, patients most likely would not get insurance coverage, since private insurers generally cover only ACIP-recommended shots. Federal programs such as Vaccines for Children and Medicaid also rely on ACIP guidance to determine distribution. Public rollout would be severely limited with no official federal guidance on who should receive the vaccine.
“That is a serious concern,” Levy said.
For now, the approval itself marks a milestone: the first mRNA flu shot to reach the U.S. market, and a test of whether the speed and flexibility that defined the Covid vaccine effort can translate into better protection against a virus that kills tens of thousands of Americans every year.
— Aisha Mensah, health desk, AXO News