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mRNA vaccines have played an important role in helping the nation fight COVID-19. Soon, they may help us battle seasonal flu as well.
But what exactly are mRNA vaccines, and how do they protect us?
If the term "mRNA" sounds overly technical, don’t worry—it’s easier to understand than you might think. 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 and how they work.
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 about mRNA flu vaccines? While not yet available for public use, mRNA-based influenza vaccines are currently being developed and tested.
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® (2024-2025 Formula): Spikevax is the brand name for the Moderna COVID mRNA vaccine approved for people age 12 and older. 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® (2024-2025 Formula): COMIRNATY is the brand name for the Pfizer-BioNTech COVID mRNA vaccine approved for people age 12 and older. 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 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. 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 COVID-related complications, hospitalization, and death. In addition, mRNA vaccines are shown to be better than natural infection at fighting future COVID infections.1
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.2
Since then, these mRNA vaccines have been regularly updated to guard against the latest circulating strains of the virus. In a November 2024 update, the Centers for Disease Control and Prevention (CDC) reported that the 2024–2025 vaccine formulas were expected to protect well against the leading strains and emerging variants.
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:
- 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.
- 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).
- 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.
- 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. For 2024-2025, CDC recommends a COVID vaccine for most adults age 18 and older. Talk to your health care provider about the best timing and frequency of your updated COVID vaccine. Development of an updated 2025-2026 vaccine is now underway and will be available in the fall of 2025.
The CDC Advisory Committee on Immunization Practices (ACIP) voted unanimously to recommend the updated 2025-26 flu vaccine 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 updated 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.
Sources
1. 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
2. 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
