For the first time, adults age 50 and older in the United States can get an mRNA flu vaccine.
The U.S. Food and Drug Administration (FDA) approved mFlusiva®, the first mRNA flu vaccine, in August 2026. Moderna makes mFlusiva. It uses the same basic vaccine technology as mRNA COVID-19 vaccines. But it targets influenza.
Unlike traditional flu vaccines, mFlusiva does not contain a live or killed influenza virus, or pieces of the virus. Instead, it uses messenger RNA (mRNA). This gives temporary instructions to your immune system, your body’s natural defense system. The instructions help it learn to recognize influenza.
This new approach might even have an edge over traditional flu vaccines.
“There is some evidence that suggests mFlusiva may offer somewhat better protection against the flu than traditional flu vaccines,” says Rebecca Choudhury, MD, Assistant Professor of Medicine (Infectious Diseases), Icahn School of Medicine at Mount Sinai.
How does mFlusiva work? How well does it protect against the flu? What do we know about safety and side effects? Dr. Choudhury explains the new mRNA flu vaccine and gives advice on getting your flu shot.
Rebecca Choudhury, MD, Assistant Professor of Medicine (Infectious Diseases), Icahn School of Medicine at Mount Sinai
How does mFlusiva work, and how is it different from traditional flu vaccines?
Traditional flu vaccines show the influenza virus or parts of it to the immune system. This teaches the immune system to recognize and fight the virus later. Depending on the vaccine, that may mean a killed virus, a weakened virus, or pieces of the virus.
mFlusiva is an mRNA vaccine. It does not contain a living or dead virus. It also does not contain viral parts. The vaccine uses messenger RNA designed to produce influenza surface proteins called hemagglutinin.
An image of the mFlusiva mRNA flu vaccine. Image credit: Moderna
It’s the same basic principle used by mRNA COVID-19 vaccines. But the target is different. COVID-19 vaccines tell cells to make the coronavirus spike protein. mFlusiva tells cells to make an influenza surface protein.
“This flu vaccine is creating a different protein, but the principle of how it works is the same,” says Dr. Choudhury.
Is mFlusiva more effective than traditional flu vaccines?
In one trial in adults age 50 and older, about 2 percent of people who received mFlusiva developed influenza confirmed by lab testing within six months of vaccination. By comparison, 2.8 percent of people who received a standard-dose flu vaccine developed influenza. The mFlusiva group had a 27 percent lower rate of flu.
For adults 65 and older, there is an important caveat. People in this age group typically receive a high-dose or adjuvanted flu vaccine rather than the standard-dose vaccine used in this trial. An adjuvanted vaccine has an added ingredient that helps the vaccine work better.
Studies comparing the immune response to mFlusiva with a high-dose flu vaccine have been encouraging. Immune response means how the body reacts to a vaccine to build protection.
“However, a stronger immune response does not necessarily mean better protection against actually getting the flu,” Dr. Choudhury notes.
Another study is expected to directly compare clinical outcomes between mFlusiva and a high-dose flu vaccine in adults 65 and older.
Is mFlusiva safe? What are the side effects?
Clinical trials so far suggest mFlusiva has a safety profile similar to traditional flu vaccines for serious adverse events. These are harmful or unexpected medical problems or side effects.
In a trial comparing mFlusiva with a standard-dose flu vaccine, serious vaccine-related adverse events were very rare. They occurred at similar rates in both groups.
Researchers also looked closely at heart-related events because of concerns previously raised about mRNA COVID-19 vaccines.
One participant who received mFlusiva developed cardiomyopathy and pericarditis. These are two heart-related conditions. This happened about three months later. It was unclear whether the vaccine caused them. One participant in the traditional flu vaccine group also developed pericarditis.
Dr. Choudhury says current data do not show a higher risk of these events with mFlusiva than with traditional flu vaccines.
The main difference so far is short-term side effects. Injection-site reactions, headaches, body aches, and fatigue occurred more often with mFlusiva than with traditional flu vaccines. This was seen across multiple studies.
“These symptoms are generally relatively mild, they go away on their own without any sort of treatment,” Dr. Choudhury says.
What are the advantages of an mRNA flu vaccine?
“The advantages are less so in how the vaccine itself works, and more so in how the vaccine is made,” Dr. Choudhury says.
Each year, scientists must predict which influenza strains will circulate months before flu season. Traditional flu vaccines take several months to produce. That can make it hard to change the vaccine if the strains that circulate are different from those expected.
Because mRNA vaccines do not rely on growing influenza virus in a lab, they can be produced more quickly. Dr. Choudhury says this could give vaccine makers more flexibility. They can update an mRNA vaccine when an unexpected flu strain begins circulating.
That flexibility could help produce flu vaccines that more closely match the strains actually circulating. It could also potentially improve how well seasonal flu vaccines protect people.
Who can get mFlusiva, and who may want to consider it?
mFlusiva is approved for adults age 50 and older. Based on the evidence so far, Dr. Choudhury says adults ages 50 to 64 may have the clearest reason to consider it.
People ages 50 to 64 typically receive a standard-dose flu vaccine. That was the same type used in the clinical trial. The trial found a lower rate of influenza among mFlusiva recipients.
Dr. Choudhury says mFlusiva may be especially worth considering for adults ages 50 to 64 with long-lasting (chronic) health conditions. These conditions can raise the risk of severe influenza. They include high blood pressure (hypertension), diabetes, chronic kidney or liver disease, obesity, or chronic lung disease.
Adults 65 and older can also receive mFlusiva. However, researchers are still gathering stronger clinical evidence. The studies compare mFlusiva with the high-dose or adjuvanted flu vaccines typically recommended for this age group.
Still, choosing between vaccines should not stop you from getting vaccinated.
“Ultimately, the best flu vaccine is the flu vaccine that you can get,” Dr. Choudhury says. If mFlusiva is not easy to get, she recommends getting an appropriate flu vaccine from your doctor’s office, pharmacy, or workplace rather than going without vaccination.
Can an mRNA flu vaccine change your DNA?
No. The mRNA in mFlusiva cannot change your DNA. It also cannot become part of your genetic code.
Dr. Choudhury says this has confused some people. Some worry that mRNA could reprogram their genetic code. But that’s not how the technology works.
Like other mRNA vaccines, mFlusiva gives cells temporary instructions to make a specific protein. Here, that protein is an influenza surface protein. The mRNA is then quickly broken down by the body.
“The mRNA in mFlusiva cannot become part of your genome,” says Dr. Choudhury.
When should you get your flu shot?
Flu season typically begins around October. Infections often peak around December. But the timing can vary from year to year.
Your immune system needs about two weeks after vaccination to build protection. Dr. Choudhury recommends planning ahead. The same timing applies to mFlusiva.
“I typically get the flu vaccine myself around early October,” Dr. Choudhury says.
Getting vaccinated is important even if you don’t consider yourself at high risk for serious problems from the flu. Influenza can cause severe illness that requires a hospital stay. Even a less serious case can leave you sick in bed for a week or longer.
“Getting your flu shot is a very easy, safe and effective step you can take to reduce your risk of getting sick and reduce your risk of making others sick,” Dr. Choudhury says.