A new flu shot: What to know about the mRNA influenza vaccine
September 17, 2026
Every fall, millions of Americans heed the call to get their annual flu shot. Getting vaccinated reduces the risk of severe illness, hospitalization, and death from influenza.
This fall, adults 50 and older have a new option to protect their health. In August 2026, the Food and Drug Administration (FDA) approved the first flu vaccine in the U.S. to use messenger ribonucleic acid (mRNA) technology.
In this vaccine, named mFLUSIVA, the mRNA provides temporary instructions that help the body’s cells produce a harmless flu protein, allowing the immune system to recognize the virus and build protection against future infection.
This technology has been studied since the 1960s and has been proven safe and effective for use in human medicine since the early 2000s. Vaccines using mRNA technology helped save hundreds of thousands of lives during the COVID-19 pandemic. And it’s currently being tested in a new treatment for melanoma, the most aggressive form of skin cancer.
The Centers for Disease Control and Prevention (CDC) estimates that flu infections in the U.S. cause 120,000-710,000 hospitalizations and 6,300-52,000 deaths each year. The people most at risk are older adults, people with compromised immune systems, and children.
While no vaccine can prevent every infection, getting vaccinated against the flu helps contain the spread of the virus and reduces preventable hospitalizations and deaths from influenza.
This year, like every year, we recommend that anyone who is eligible get vaccinated against influenza. People over 50 can choose from several flu vaccine options, including mFLUSIVA, which is produced by Moderna, maker of one of the first COVID-19 vaccines.
How does the mRNA flu vaccine work?
All flu vaccines teach the immune system to recognize the influenza virus, but they deliver that information in different ways. Traditional flu shots may contain an inactivated form of the virus or purified viral proteins. Some flu vaccines are made using eggs; others use cell-based or recombinant manufacturing methods.
The mFLUSIVA vaccine uses lipid particles, which are tiny shells made of fat-like molecules, to carry three mRNA sequences into your cells. Each mRNA sequence contains instructions for making hemagglutinin, a protein found on the surface of the flu virus.
Once your cells briefly make these proteins, your immune system recognizes them as foreign and produces antibodies to protect against them. Those antibodies help your immune system respond more quickly if you are later exposed to a matching strain, reducing your risk of infection and, if you do get the flu, lowering the risk of severe illness.
The mRNA breaks down naturally after delivering its instructions; it does not enter the cell’s nucleus or alter your DNA. The mFLUSIVA vaccine contains no whole flu virus and cannot cause influenza. The 2026-27 formula contains no egg protein, antibiotics, or preservatives.
Is the mRNA flu vaccine effective?
In a phase three clinical trial, more than 40,000 adults 50 and older received either mFLUSIVA or a licensed, standard-dose, inactivated flu vaccine. Data showed that 2% of people who received mFLUSIVA developed flu illness compared with 2.8% of those who received a standard-dose vaccine. That translates to about a 27% lower relative risk of flu illness in the mFLUSIVA group, compared to standard influenza vaccination.
Using mRNA technology in the flu vaccine could improve how we respond to this ever-changing virus. It is easier to copy viral mRNA sequences than it is to grow large amounts of the influenza virus in a lab. That means manufacturers may be able to update seasonal flu vaccines more quickly and respond faster when new strains emerge.
Which flu vaccine should I choose after age 50?
In clinical trials for mFLUSIVA, participants included adults who were more likely to develop serious complications with the flu. This is why the new vaccine is currently approved only for people 50 and older. For adults ages 50-64, the CDC does not prefer one licensed, age-appropriate flu vaccine over another. The mFLUSIVA shot is one option alongside inactivated and recombinant vaccines. Medical history, availability, prior reactions, and personal preference can guide the choice.
Vaccine recommendations become more specific at age 65. The CDC has historically recommended one of three enhanced vaccines for adults 65 and older:
- Fluzone High-Dose inactivated vaccine
- Flublok recombinant vaccine
- Fluad adjuvanted vaccine
The mFLUSIVA vaccine is now approved for people in this age group. Talk with your doctor about the best flu vaccine option for you. If the vaccine you prefer is not available in your area, choose another age-appropriate option. The most important step is to get vaccinated each year.
Are there side effects with the mRNA vaccine?
With any vaccine, there is a chance for a short-term immune response – that is a sign the injection is doing its job of activating your immune system. The most common reactions with the mFLUSIVA vaccine are mild and are similar to standard flu shot side effects:
- Tenderness at the injection site
- Mild fatigue
- Headache
- Muscle or joint aches
- Chills
- Underarm tenderness or swelling
About 75% of mFLUSIVA recipients reported at least one expected short-term reaction, compared with 47% of those who received the standard-dose vaccine. Most side effects were mild or moderate and lasted around two days.
When should I get a flu vaccine?
The CDC recommends that most eligible people get vaccinated against the flu in September or October. This is because the immune system needs about two weeks to build protection. Getting vaccinated too early can allow that protection to wane before flu season ends. We generally advise people at higher risk and those who live with a vulnerable family member to aim for October.
You may be at higher risk for serious flu complications if you:
- Are younger than 5 or age 50 or older, particularly 65 or older.
- Are pregnant or gave birth within the past two weeks.
- Have a chronic condition such as asthma, chronic obstructive pulmonary disease, heart disease, diabetes, kidney or liver disease, a blood disorder, or a neurologic condition.
- Have a weakened immune system because of an illness or medication.
- Live in a nursing home or other long-term care facility.
- Have a body mass index (BMI) of 40 or higher.
Do not wait until local case counts spike to get vaccinated. Surveillance reports lag behind transmission, and the immune system needs about two weeks to build its full response. Flu often circulates for months, and adults generally need one flu dose per season.
Vaccination is your strongest defense against severe flu, and everyday habits provide another layer of protection. Cough or sneeze into the inside of your elbow rather than into your hands. Wash your hands often with soap and water, and avoid touching your eyes, nose, and mouth.
Consider wearing a mask in crowded indoor spaces when flu activity is high. If you are sick, stay home when possible and wear a mask if you must be around others.
Which other vaccines should I get this fall?
Along with your flu shot, older adults should also get a few more vaccines to protect against respiratory infections, including:
- COVID-19: Get an updated vaccination, especially if you are 65 or older or have a condition such as diabetes or obesity that increases the risk of severe disease.
- Respiratory syncytial virus (RSV): The CDC recommends one dose for all adults 75 and older and for adults 50-74 who have an increased risk of RSV.
- Pneumonia: The pneumococcal vaccine protects against various forms of the disease. Adults 50 and older who have never had a vaccine should get one as should those age 19-49 with respiratory risk factors such as a compromised immune system.
Most vaccines, including those on this list, are safe to get together in one visit. Talk with a doctor about which vaccines are recommended for you and when to get them.
Getting vaccinated is one of the best, most proven ways to avoid serious flu-related illness this season. By choosing to get any flu vaccine, you are taking an important step to protect yourself, your loved ones, and the vulnerable people in your community.
To talk with an expert about flu vaccines, make an appointment by calling 214-645-8300 or request an appointment online.
