mRNA vaccines have played an important role in helping the nation fight COVID-19. Now, they will help us battle seasonal flu as well. The FDA has approved Moderna's mFLUSIVA, the first mRNA flu vaccine for adults age 50 and older in the U.S. But what exactly are mRNA vaccines, and how do they protect us?

At their core, mRNA vaccines teach our body’s immune system how to recognize and defend itself from harmful viruses. In this article, we'll break down what mRNA vaccines are, how they work, and why they’re considered safe and effective.

mRNA Vaccine Safety at a Glance

What does mRNA stand for?

mRNA stands for messenger ribonucleic acid (RNA). It’s a molecule that carries instructions from your DNA (the genetic blueprint in your cells) to the parts of your cells that make proteins. mRNA has always been present in all human cells. 

What is the role of messenger RNA?

True to its name, mRNA acts like a messenger to the “machinery” in our cells that makes protein. It teaches our cells how to make proteins in a natural, essential process called protein synthesis. Proteins are the building blocks that help our bodies function properly, from growing muscles to fighting off infections.

How do mRNA vaccines work?

These vaccines use a piece of mRNA that tells your cells how to make a harmless viral protein called an antigen. An antigen is a part of a pathogen that could make you ill—but don’t worry; it's been changed in a way that makes it unable to cause disease.

When our cells start making this antigen, our immune system recognizes it as a foreign invader. In response, it produces antibodies that target the antigen. Antibodies are special proteins that help us fight illness by recognizing and neutralizing harmful pathogens before they make us sick. These antibodies can linger in our bodies for many months.

For example: When a COVID mRNA vaccine is injected into your upper arm at a health clinic, pharmacy, or your doctor’s office, the mRNA enters cells located near the injection site. It then instructs those cells to begin making copies of the S protein (antigen) found on the surface of the COVID-19 virus. Once your immune system recognizes these S proteins, it begins producing antibodies to the COVID virus. Here’s the payoff: Later on, if you’re exposed to COVID by someone you know or in a crowded public space, you have antibodies ready to fight the virus and help you ward off severe disease.

What is the new mRNA flu vaccine?

The FDA has approved Moderna's mFLUSIVA, the first mRNA flu vaccine for adults age 50 and older in the U.S., after clinical trials demonstrated its strong efficacy in preventing the flu in older adults compared to a standard-dose licensed flu vaccine. For adults age 65 and older, the vaccine received accelerated approval, which means more studies are happening to confirm its long-term benefits.

Getting a flu shot every year is the best way to reduce your risk of severe illness from the flu. This is especially true for older adults, who are at greater risk of serious flu complications, including hospitalization and death. But because flu viruses change over time, and the traditional flu vaccine takes many months to formulate, the shot’s effectiveness can vary from one season to the next.

Thanks to its mRNA technology, the new mFLUSIVA flu vaccine offers a key advantage: it can be updated more quickly if new strains emerge, helping it better match the viruses circulating during flu season.

When will the new mRNA flu vaccine be available? mFLUSIVA is expected to be available to eligible adults for the 2026–2027 flu season. But it’s not yet clear how widely the vaccine will be offered or whether insurance will cover it, especially for adults age 65 and older. Those details are still being worked out.

Which COVID vaccine uses mRNA?

There are two types of COVID mRNA vaccines approved by the U.S. Food and Drug Administration (FDA) for use in adults and adolescents:

• Moderna Spikevax®: Spikevax is the brand name for the Moderna COVID mRNA vaccine approved for people age 65 years and older, or 6 months through 64 years at high risk for severe COVID-19. It was developed by the pharmaceutical company Moderna in collaboration with the U.S. National Institute of Allergy and Infectious Diseases (NIAID).
• Pfizer-BioNTech COMIRNATY®: COMIRNATY is the brand name for the Pfizer-BioNTech COVID mRNA vaccine approved for people age 65 years and older, or ages 5 through 64 at high risk for severe COVID-19. It was developed by the pharmaceutical companies Pfizer and BioNTech.

What is the difference between traditional vaccines and mRNA vaccines?

One major difference between traditional vaccines and mRNA vaccines is in the way they “teach” our immune system to fight off a virus.

Conventional vaccines (such as the standard flu vaccine, RSV vaccine, or measles vaccine) introduce antigens directly into our body using a weakened or inactivated portion of a virus. In contrast, mRNA vaccines instruct cells to make these antigens themselves.

What's more, traditional vaccines and mRNA vaccines are developed at different speeds. Most conventional vaccines are made from viruses grown in labs. This involves a complex, time-consuming process that can take many months—or even years. For example, most (96%) standard flu vaccines are still made using a decades-old egg-based process. Since the flu virus can change after the vaccine is developed, the vaccine may not always be the right match for the strains circulating during flu season.

mRNA vaccines, on the other hand, are produced from a DNA template and are easily replicated. Creating an experimental batch of a new mRNA vaccine can take as little as a week—and it can quickly be scaled up as needed.

Plus, the nature of mRNA vaccines makes them highly adaptable to a variety of pathogens. This means they have the potential to combat a wide range of diseases.

As a newer class of vaccines, mRNA vaccines allow for fast, targeted, cost-effective vaccine development against both viral outbreaks and emerging pathogens. We saw this when the mRNA COVID vaccines first became available less than one year after the virus began spreading globally.

Are mRNA vaccines effective?

While no vaccines are 100% effective in preventing infection, mRNA vaccines are found to be highly effective in preventing severe flu- and COVID-related illness, hospitalization, and death:

• Flu: In a large clinical trial of mFLUSIVA involving nearly 41,000 adults age 50 to 64, the new vaccine was 26.6% more effective at preventing the flu than a standard flu vaccine.¹ A June 2026 study found that Moderna’s mRNA flu vaccine may produce a stronger, longer-lasting immune response than traditional flu vaccines.²
• COVID: mRNA vaccines are shown to be better than natural infection at fighting future COVID infections.³ Early trials showed a 94.1% efficacy rate for the Moderna COVID vaccine (mRNA-1273) and a 95% efficacy rate for the Pfizer/BioNTech COVID vaccine (BNT162b2) in providing protection against COVID.⁴ Since then, these mRNA vaccines have been regularly updated to guard against the latest circulating strains of the virus. 

Are mRNA vaccines safe?

Before being authorized for public use, mRNA vaccines undergo rigorous testing in multiple phases of clinical trials—just like traditional vaccines. These trials involve tens of thousands of participants and are closely overseen by agencies such as the FDA.

Here are four reasons why mRNA vaccines are considered safe for older adults:

1. Well-tested technology: Although mRNA vaccine technology is relatively new for widespread use, scientists have been studying these types of vaccines for more than 30 years. The speed of COVID-19 vaccine development during the pandemic was largely due to the research already in place.
2. No interference with DNA: Contrary to what you might have heard, mRNA vaccines do not cause genetic mutations or cancer. In fact, they never enter the nucleus of cells where our DNA is stored. Instead, they only deliver the instructions for making a specific protein (antigen).
3. Temporary presence in the body: The mRNA in vaccines doesn’t stay in our body for long. After the cells make the protein, the mRNA is quickly broken down and flushed out.
4. Ongoing safety monitoring: Even after mRNA vaccines are authorized, their safety continues to be monitored closely through various surveillance systems. This helps ensure any rare side effects are quickly identified and addressed.

Like all vaccines, mRNA vaccines can cause side effects. The most common reported side effects are mild and include pain, redness, and swelling at the injection site.² Some people may also experience fatigue, body aches, fever, and chills that commonly last no more than 24-48 hours.

Make sure you’re up to date on your COVID and flu vaccines

As part of your healthy aging and wellness routine, consider getting vaccinated against COVID and the flu this year. 

Vaccines are one of the best ways to protect our health and maintain a good quality of life throughout the lifespan.

• COVID: Vaccination against COVID is a personal decision you should make with your health care provider. If you’re age 65+ or you have a chronic health condition (e.g., diabetes, heart disease), it’s particularly important to get your COVID shot since it lowers your risk of serious illness, hospitalization, and death. At NCOA, we recommend older adults consult with their health care team and stay up to date by getting the COVID, flu, and RSV vaccines. It’s still the best way to avoid severe outcomes and protect health, independence, and quality of life.
• Flu: CDC recommends an annual flu shot for everyone age six months and older. The best time for older adults to receive the flu shot is September or October. Getting vaccinated before cold and flu season, like in the summertime, can result in immunity wearing off too early.

Where can I get my COVID and flu vaccines?

Check with your primary health care provider to find out if they have COVID and flu vaccines available. If not, try the following:

• Call your neighborhood pharmacy. While some pharmacies offer walk-in vaccinations, others require you to schedule an appointment on their website. Your pharmacist can answer any questions you have about the COVID and flu vaccines.
• Contact your local health department. Your community likely offers free vaccine clinics at senior centers and other nearby locations where you can get your COVID and/or flu shot. You may have to register online and reserve a time slot in advance.
• Visit the CDC website. Learn how to find a convenient location to get your COVID and/or flu vaccine and what to expect at your appointment.

Frequently asked questions (FAQ)

Do mRNA vaccines change your DNA?
No. mRNA vaccines do not change your DNA. They never enter the part of your cells where DNA is stored. Instead, they give your cells temporary instructions to help your immune system recognize and fight a virus. Once those instructions are used, the mRNA quickly breaks down and leaves your body.

Is the mRNA flu shot better than the regular flu shot?
Maybe. In a large clinical trial, Moderna's new mRNA flu vaccine provided stronger protection against the flu than a standard flu vaccine in adults age 50+. More research is underway to confirm its efficacy in adults age 65+. Both traditional and mRNA flu vaccines must meet the FDA's strict standards for safety and effectiveness before they can be approved.

What are the side effects of mRNA vaccines?
Like other vaccines, mRNA vaccines can cause temporary side effects as your immune system responds. These include soreness, redness, or swelling where you got the shot, along with tiredness, headache, muscle aches, chills, fever, or nausea. These side effects are usually mild to moderate and go away within a day or two. Serious side effects are rare.

Sources

1. Isabel Leroux-Roels, MD, et. al. Efficacy and safety of an mRNA seasonal influenza vaccine in adults. The New England Journal of Medicine. May 6, 2026. Found on the internet at https://www.nejm.org/doi/full/10.1056/NEJMoa2516491

2. Hanover C. Matz, et. al. mRNA-based influenza vaccine expands the B cell response breadth in humans. Nature Immunology. June 15, 2026. Found on the internet at https://www.nature.com/articles/s41590-026-02569-5

3. Stanford Medicine. mRNA vaccine beats infection for key defense against COVID-19, Stanford Medicine scientists find. March 28, 2023. Found on the internet at https://med.stanford.edu/news/all-news/2023/03/vaccine-covid-infection.html

4. ​​​​​​​Yahya F. Jamous, et. al. The Safety and Effectiveness of mRNA Vaccines Against SARS-CoV-2. Cureus. September 15, 2023. Found on the internet at https://www.ncbi.nlm.nih.gov/pmc/articles/PMC10588549/#REF12