Here’s what the first mRNA flu vaccine could mean for flu season

mRNA flu shots have officially arrived.

On August 5, the U.S. Food and Drug Administration approved the first influenza vaccine that uses the same technology underpinning COVID-19 shots. The flu vaccine, called mFlusiva and produced by Moderna, will be available for people ages 50 and older at select drug stores ahead of the upcoming flu season, the Massachusetts-based company said.

Influenza kills thousands of people in the United States each year and hospitalizes tens of thousands more. The FDA’s approval is based on a study of 40,000 individuals who got either a dose of mFlusiva or a conventional flu shot. The mRNA flu shot group experienced 27 percent fewer cases, clinical trial results showed.

Depending on the year, conventional vaccines are anywhere from 40 percent to 60 percent effective at preventing infection. That’s often due to a mismatch between predictions for what flu strain will be circulating in the fall and which one actually shows up.

Other research, published in June in Nature Immunology, found that the mRNA vaccine generates a stronger and longer-lasting immune response than conventional flu vaccines.

Science News spoke with study coauthor Hanover Matz, an immunologist at WashU Medicine in St. Louis, about the new vaccine and its implications for future flu seasons. This conversation has been edited for clarity and length.

SN: How is Moderna’s mRNA flu vaccine different from conventional flu vaccines?

Matz: The conventional flu vaccine is typically generated in chicken eggs, and it’s what we call an inactivated flu vaccine. Essentially there are pieces of the virus that are used to teach your immune system how to fight flu, and because the virus is raised in chicken eggs, it takes a long time to generate that vaccine. This is an mRNA-based vaccine, which provides genetic information for how to make the proteins of the flu virus, and then that teaches your immune system how to fight it.

SN: What are the benefits of getting the mRNA flu vaccine versus the conventional one?

Matz: It can be produced much faster than the conventional flu vaccine, and this is very useful if the virus changes during the flu season.

For producing the egg-based vaccine, policy makers need to determine what the most likely strains of the flu virus are going to be for the fall season in the Northern Hemisphere. Typically, they need to start that production well before the fall to get the vaccine doses ready. If there’s a mismatch in strains, there’s really no way they can go back and update the vaccine and change it. The production just takes too long. With an mRNA-based vaccine, you could feasibly cut down that production time to a couple of months. [Manufacturers] have the potential to improve the speed with which they could update the vaccine if that strain mismatch became a problem during the during the flu season.

It also seems to generate a very strong immune response against the flu virus. In our study, people who received the mRNA-based vaccine had much higher levels of antibodies against flu one month after vaccination. And those higher levels persisted for six months, which suggests that there is an increase in the duration of the protection.  

SN: Why is the mRNA flu vaccine available only to people ages 50 and older? 

Matz: In the clinical trials that Moderna conducted, they were able to show that this vaccine was better at providing protection in people who were over 50, and especially people who were over 65 years of age. So [the company] got accelerated approval for that age group, and this is the age group that policy makers are most focused on for providing protection against flu because they’re more at risk [for severe illness and death] than the general population.

SN: When do you think it will become widely available?

Matz: I don’t know what Moderna’s timeline is. I suspect that they’re probably working on [getting approval for use in people under 50]. What I can say is that all flu vaccines are beneficial to people, regardless of age. If you get a flu vaccine, and you’re protected against flu, you can help reduce transmission of the virus to people who are more at risk. It’s always beneficial for people to get the flu shot, regardless of age.

SN: How might the new vaccine impact future flu seasons? Are we likely to see fewer severe cases and deaths?

Matz: Potentially. That was one of the outcomes from the clinical trials that Moderna conducted and how this got approval in people over 50.

One of the things that’s going to be interesting for future research is to see whether an mRNA-based vaccine can cut down on flu transmission rates. That’s one of the most important things we think about for respiratory viruses: Not only does this vaccine protect an individual but does it stop the virus from spreading? If we can stop the virus from spreading, we can definitely cut down on rates of hospitalization.