mFlusiva, or mRNA-1010, is a new type of flu vaccine made by Moderna to protect against flu. It has recently received final approval and will hopefully be available this fall for adults over 50.
What is mFlusiva and how is it different from the other flu vaccines?
This new type of flu vaccine is based on the same mRNA technology that was used in COVID vaccines. mRNA is the directions, or blueprints, for making a building block in the body. Just like the COVID vaccine contained the mRNA blueprint for a part of the virus called spike. Spike allows the virus to grab on and infect. Flu has a similar part called hemagglutinin, or HA for short. mFlusiva contains the mRNA for HA. In fact, three different HA mRNAs are included to provide protection against three different strains of flu. Therefore, it is called a trivalent vaccine.
🚨 Nerd alert: There are two types of flu that infect humans, Flu A and Flu B. Flu A is much more common and changes more often. There are also two major molecules on the surface of the virus that our immune system responds to, HA and something called neuraminidase, or NA. Flu viruses are grouped as A and B, and then described by their HA and NA type. All available flu vaccines are designed to protect against Flu A, H1N1, Flu A H3N2, and Flu B.
The four types of flu vaccines are made differently, but all protect against severe influenza disease and death.
❎ Inactivated: This vaccine is made by growing the virus and then inactivating it so it is no longer infectious. It is injected into your arm. It is available for everyone over 6 months of age. A high-dose version is available for people over 65 because their immune system needs a little extra help to respond to the vaccine. According to the CDC this type of vaccine may still be given to people with egg allergies. If you have an egg allergy, you may wish to consult with your trusted clinician. This type of vaccine can’t give someone the flu.
🔄 Recombinant: This vaccine is made by making just the HA without growing the virus, and purifying it. It has 3 times the amount of HA than what is found in the inactivated vaccine. It is approved for use in people over 9 years of age and is safe for people with egg allergies. This type of vaccine can’t give someone the flu.
🦠Live attenuated: This vaccine is made by creating a weakened, also called attenuated, version of the virus. It is approved for people from age 2 to 49 with no chronic medical conditions. It is sprayed in your nose. This virus does still infect, and can cause flu-like symptoms, but does not cause serious influenza disease.
🧬 mRNA: This vaccine is made by producing an mRNA to just the HA and packaging it in a fatty shell. It is injected into your arm. It will soon be available for people over 50. Like the COVID vaccine, this vaccine can cause flu-like symptoms and other mild reactions, which, according to the clinical trial data, were more common in people who received the mRNA vaccine compared to the traditional flu vaccine. However, in both groups the reactions were mostly mild and lasted 1-2 days. This type of vaccine can’t give someone the flu. The clinical trial showed better protection: 27% fewer study participants who received the mRNA vaccine got sick than those who received the standard vaccine. So, this vaccine is a great new option to protect against influenza disease.
Which type of flu vaccine should I get and when should I get it?
The best answer to this question is get the flu vaccine that is available to you. Trying to find a specific type of vaccine is not likely to make a big difference in your protection. If you are over 50, would like to get mFlusiva, and it is available to you, go for it. But any protection is better than no protection. As for when to get the vaccine, you should get it when you can. While you can get infected with flu any time of year, most cases happen between October and May with cases peaking between December and February. Therefore mid-October to early November is a great time to get your vaccine. There are some situations where it will make sense to plan. For example, you should get your vaccine at least 2 weeks before times where your exposure to the flu virus is increased– like traveling by plane, going to a large party, or going to a children’s birthday party. They also include when you will be around vulnerable people like infants, people undergoing cancer treatment, or older people. This timing is important because it takes about 2 weeks to be fully protected after receiving a vaccine.
If you are over 65, you should consider getting either mFlusiva or the high-dose flu vaccine. These are recommended for this age group because the older we get, the weaker our immune system’s response is to vaccines.
As always, if you have any medical concerns, discuss your options for protection against flu with your clinician.
Can I get my flu and COVID vaccine at the same time?
Yes, many pharmacies and clinicians can administer both vaccines during the same visit. There is no evidence that there is any different protection if you receive them at the same time or on different days.
How was mFlusiva tested?
The main approval was based on a large clinical trial with over 40,000 adults during the 2024-2025 flu season. About half the participants were 50-64 and half were over 65. They were randomized to receive either mRNA1010 (mFlusiva) or the standard inactivated flu vaccine. The study showed that the vaccine was safe and provided 27% better protection against flu illness compared to the standard flu shot. Side effects were more frequent in people who received the mRNA vaccine than the standard flu shot, but those reactions were mostly mild and lasted 1-2 days. However, it is normally recommended that adults over 65 receive a high dose vaccine. Therefore, for the accelerated approval in adults over 65 they used data from an earlier trial specifically testing mFlusiva versus both the standard vaccine and the high-dose vaccine in adults over 65. The test showed that mFlusiva worked as well as the standard vaccine in adults 50-64 and the high-dose vaccine in adults over 65. The important takeaway is that the new mFlusiva vaccine works as well, or better, than the standard flu vaccine you normally get.
Why wasn’t mFlusiva tested against placebo?
This is a reasonable question. There are three main reasons. First, it is unethical to use a placebo in a clinical trial when a known treatment or vaccine is available since not providing the currently available treatment/vaccine leaves a study participant vulnerable and could cause harm (read more about ethics in clinical trials in a post by Nerdy Girl Sandy). Second, in these types of clinical trials where a new vaccine is tested against an existing vaccine, researchers test for something called non-inferiority. That is just a fancy way of saying they need to know if what they are testing is at least as good as the currently available vaccine. We certainly don’t want to approve something that is worse than what we currently have! Third, if they only tested if the vaccine worked compared to placebo, we would be left wondering if the new vaccine is basically the same as the old one, or if it actually protects better. For the flu vaccine, researchers already know the available standard flu vaccine works, so if the new vaccine works as well or better than the one they compared it to, it certainly would have worked better than placebo. Because they carried out the trial comparing mFlusiva to the standard inactivated vaccine, we now know that mFlusiva works even better and we can make an informed decision about which flu vaccine to get.
The bottom line is that flu is nothing to sneeze at and there are many ways to protect you from serious influenza disease. The best option is the one you choose to protect yourself and your loved ones.
Stay healthy and wise,
Those Nerdy Girls
Resources:
Clinical trial testing mFlusiva in adults over 50
Earlier clinical trial testing mFlusiva in adults over 18
AP – New kind of flu shot is on the way as the FDA approves Moderna’s mRNA-based vaccine
