The US Food and Drug Administration has approved the nation’s first mRNA-based flu vaccine – from Moderna – for people 50 and older, reports CNN.
Initially, after the Trump administration slashed funding for mRNA vaccine development, the FDA had declined Moderna’s request to review the shot. But in June, the agency’s independent vaccine advisers unanimously voted that the vaccine’s benefits outweigh its risks.
Named mFlusiva, it is hoped to be available within the next few weeks.
How the mRNA flu vaccine is different
Traditional flu shots use inactivated or weakened forms or pieces of the virus to train the immune system to recognise the live virus if it enters the body, but mRNA vaccines use a piece of mRNA, that encodes for a viral protein.
When you receive an mRNA vaccine, your body gets the instructions to make a copy of that protein, which then generates the immune response that prepares you to fight off future infections.
The flu virus is constantly mutating, and annually, scientists aim to match the strains in the vaccine to the ones most likely to be dominant in the coming flu season.
“Sometimes there’s a mismatch between what was selected, despite best efforts, and what the dominant circulating strain is,” said Dr William Schaffner, a professor of infectious diseases at the Vanderbilt University Medical Centre. How closely matched the flu vaccine is to the dominant strain of the season is part of what accounts for the year-to-year changes in the shot’s effectiveness.
One limit to the currently used flu vaccine platform is that the selection of what virus strain to include must happen around February, about six months before the shots are administered. Currently, flu vaccines are manufactured by growing the influenza virus in cells or chicken eggs.
“That’s a huge challenge because it is often limiting in terms of how fast and how much vaccine we can make,” said Dr Michael Osterholm, who directs the Centre for Infectious Disease Research and Policy at the University of Minnesota.
Since mRNA vaccines can be manufactured quickly, the strain selection can occur closer to when shots are administered – in May, instead of February.
The vaccine will be available for people 50 and older, but it was given two different types of approval.
Moderna’s new vaccine was granted standard approval for people aged 50 to 64. For those older than 65 and older, it received accelerated approval.
The FDA had originally okayed Moderna’s study design for the mRNA flu vaccine but then rejected the application in February before eventually agreeing on the two-pronged approval pathway.
The agency said this year that Moderna’s application didn’t contain an “adequate and well-controlled” trial because the control arm of the study didn’t reflect the “best-available standard of care in the United States at the time of the study”.
Moderna had compared the vaccine’s efficacy in over-50s to a standard dose flu vaccine. However, guidance from the US Centres for Disease Control and Prevention recommends an enhanced dose vaccine for over-65s.
“If you are older than 65, you don’t want to compare it against a weaker vaccine,” said Dr Gregory Poland, director of research for the Atria Research and Global Health Institute in New York, who was not involved in the study on Moderna’s vaccine. “You want to compare it against one of the three vaccines preferentially used in older people.”
In the 65-and-older population, Moderna presented data showing that the vaccine has better ability to produce antibodies compared with an enhanced vaccine. The FDA granted accelerated approval under the condition that Moderna conduct a post-marketing study this coming flu season to ensure that that advantage in antibody production translates to a clinical advantage.
“I think the accelerated approval, with the obligation of the company to do some studies and to come back to the FDA with further data regarding effectiveness and safety, is entirely appropriate,” Schaffner said. “That’s been done for other vaccines, and it works out well.”
Which shot to get
Moderna’s new vaccine was found to be about 27% more effective during the 2024-25 vaccine season than standard flu shots in the company’s study, which enrolled more than 40 000 people over 50.
The mRNA vaccine did show higher rates of adverse reactions compared with the standard dose vaccine, but most – injection site pain, muscle and joint pain, nausea and vomiting, fever, headache and chills – were mild to moderate and disappeared within days.
Serious adverse events occurred at similar low rates in study participants who received the mRNA vaccine and the standard flu vaccines, and most were assessed to be unrelated to vaccination.
People with allergies to any of the ingredients or who’ve had Guillain-Barré syndrome after flu jabs in the past should not get the new vaccine.
Moderna, the Health and Human Services Department, and the CDC did not respond to a request for comment on plans for rolling out the vaccine.
According to CDC data from the 2024-25 flu season, 76.9% of hospitalisations from flu were in people over 50, even though they accounted for only 34.4% of flu-related symptomatic illnesses. Furthermore, 70.6% of deaths were in over-65s, even though they had only 8.8% of illnesses.
Flu vaccines are not designed to prevent minor illness, but they are much more effective at preventing severe illness, said Poland.
“You might have had mild flu, but you didn’t get a plastic tube down your throat and be put on a ventilator,” Poland said. “In fact, you didn’t even get hospitalised.”
CNN article – FDA approves first mRNA-based flu vaccine (Open access)
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