Key takeaways:
COVID-19 vaccines from Pfizer and Moderna use messenger RNA (mRNA) technology. mRNA is a molecule that acts like a blueprint to make specific proteins in your body. An mRNA vaccine for respiratory syncytial virus (RSV) is also available.
mRNA vaccines are different from traditional vaccines, such as flu shots. They don’t need to introduce live or inactivated viruses or bacteria into the body to work.
While there are possible side effects with any vaccine, mRNA vaccines are considered safe to use. They can’t give you COVID or RSV, either.
For many people, vaccinations have been a normal part of life since childhood. They can help prevent illness no matter your age or background.
In 2020, the COVID-19 pandemic sparked a curiosity in how exactly vaccines work. In part, that interest grew out of the fact that a new vaccine technology was being widely used for the first time.
COVID vaccines from Pfizer and Moderna vaccines use this relatively new messenger RNA (mRNA) technology. They’re the first mRNA vaccines to be FDA authorized or approved for use, and we may see more mRNA vaccines in the future.
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Here, we’ll help you understand what mRNA is, how it works, and how mRNA COVID vaccines can protect you from getting sick.
What is mRNA?
mRNA is a small molecule that’s found in all cells throughout your body. Each piece of mRNA acts like a unique set of instructions, similar to a blueprint. It tells your cells how to assemble specific proteins — or parts of a protein — by putting together building blocks (called amino acids) in a certain order.
Your cells make and use mRNA to make proteins every day. Proteins are essential to the structure and function of the human body.
What is the difference between mRNA and RNA?
mRNA is a type of ribonucleic acid (RNA) that helps make proteins. While deoxyribonucleic acid (DNA) stores your body's genetic blueprint, RNA (including mRNA) helps translate DNA's instructions into proteins.
There are three different types of RNA — mRNA, transfer RNA (tRNA), and ribosomal RNA (rRNA). They each play a different role to keep your body functioning as it should. When it comes to vaccines, mRNA is the best suited to teach your body how to protect itself from illness.
How do vaccines work, generally speaking?
A vaccine teaches your immune system how to recognize an invader, such as influenza or poliovirus. It does this by imitating an infection so your body can practice recognizing the germ and fighting it off. In some ways, a vaccine is like a training exercise for your immune system.
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Most vaccines — like the flu shot — are made from dead or inactivated virus or bacteria parts. These harmless pieces are injected into your body when you receive a vaccine. They help your immune system learn to recognize the germ without the risk of getting sick.
After you’re vaccinated, your body begins to make antibodies. These are proteins that help your body fight off a virus or bacteria. Your immune system remembers how to make these antibodies for months or even years at a time, depending on the vaccine. This can keep you from getting sick if you’re exposed to the germ in the future.
How do mRNA vaccines work, by comparison?
The mRNA COVID vaccines have a similar job as other vaccines. They aim to protect you from getting sick by teaching your body how to recognize and respond to SARS-CoV-2, the virus that causes COVID.
But mRNA vaccines do this in a different way. They do not contain dead or inactive virus parts. Instead, they contain mRNA molecules that have been designed to carry the instructions for making a part of the virus.
After you receive a Pfizer or Moderna COVID vaccine, mRNA enters your cells. Your cells read this mRNA like an instruction manual and learn how to make a part of the coronavirus — the SARS-CoV-2 spike protein. Once this happens, your immune system can step in and make antibodies that recognize this protein.
The real virus that causes COVID uses this spike protein to enter your cells. If your immune system knows what this protein looks like, it can recognize it in the future and break down the virus before it enters your cells — and causes a potentially serious infection.
What are the benefits of mRNA vaccines?
mRNA vaccines have a few potential benefits over traditional vaccines.
Typically, mRNA vaccines are easier to design and manufacture than traditional vaccines. This means mRNA vaccines can be rolled out more quickly and are adaptable to emerging strains of a virus. This is helpful in situations like outbreaks and pandemics.
mRNA vaccines also work well. They’re highly effective at preventing serious illness from an infection. Specific effectiveness numbers vary by study and vaccine, though, and may shift on a year-to-year basis.
mRNA vaccines are relatively safe to use for most people, too. Side effects of mRNA vaccines are typically mild and temporary. Serious risks, such as anaphylaxis, myocarditis (heart muscle inflammation), and pericarditis (heart lining inflammation), are rare.
Besides viral illnesses, mRNA vaccines are also being studied to help treat conditions such as cancer, autoimmune disorders, and genetic conditions.
How are mRNA vaccines made?
All vaccines are made in a lab. But scientists can generally produce mRNA vaccines faster than traditional vaccines.
This stems from how mRNA vaccines work. After you’re vaccinated, your own cells can build the SARS-CoV-2 spike protein using the mRNA’s instructions. This means vaccine makers don’t have to grow, purify, and inactivate the virus beforehand. mRNA molecules are also simpler structures than viruses and bacteria.
But one challenge is that mRNA is fragile. The mRNA has to be put inside a lipid (fat) coating for protection. Because this lipid coating is not as stable at room temperature, mRNA vaccines typically last longest when kept very cold during transport and storage.
How was mRNA vaccine technology discovered?
mRNA technology isn’t actually that new. Scientists have been interested in using mRNA-based treatments and vaccines for other viruses, like influenza and Zika, for decades.
One of the biggest challenges in the past was how to transfer mRNA into our cells. In 2005, scientists figured out how to put mRNA in a stable package and safely deliver it to our cells. This previous research — combined with worldwide collaboration — made it possible for scientists to develop mRNA COVID vaccines at record-breaking speed. The previous record was 4 years for development of the mumps vaccine. But early in 2020, Chinese scientists identified and shared the genetic structure of the novel coronavirus. This allowed scientists to start work immediately on an mRNA COVID vaccine.
Two vaccines from Pfizer and Moderna — known as Comirnaty and Spikevax, respectively — were the first mRNA vaccines to be licensed for use. A second mRNA COVID vaccine from Moderna, mNEXSPIKE, was also approved in May 2025.
Which additional vaccines use mRNA?
Another vaccine that uses mRNA technology is a respiratory syncytial virus (RSV) vaccine called mRESVIA.
mRESVIA was approved in May 2024. It works in a similar way to mRNA COVID vaccines. It contains mRNA that teaches the body how to make a part of the protein found in RSV. mRESVIA is approved for use in adults ages 60 or older to prevent illness from RSV. Certain people as young as 18 can also receive it if they have an increased risk of severe RSV.
Other mRNA vaccines are currently under development in clinical trials. For example, an mRNA vaccine for norovirus is currently being studied.
Are mRNA vaccines safe?
Yes. mRNA COVID vaccines were thoroughly tested for safety prior to being authorized and approved for use. Health experts are also monitoring their safety as time goes on. COVID vaccines are held to the same rigorous safety standards as all other vaccines used in the U.S.
Though some people may experience side effects, you cannot get COVID from a vaccine. This isn’t medically possible. Remember, mRNA vaccines do not contain a live virus. They only contain a small bit of genetic information to provide instructions to your body.
It’s also important to note that mRNA vaccines cannot change your DNA. mRNA from COVID vaccines never enters the part of the cell where your DNA lives (the cell nucleus). In fact, the mRNA doesn’t interact with your DNA at all and breaks down quickly after doing its job.
How long does mRNA last in a cell?
Typically, mRNA only lasts a few days in a cell. Once an mRNA vaccine is introduced into the body, cells quickly make copies of the spike proteins of the virus. After that, the mRNA is broken down and flushed out of the body.
The bottom line
Pfizer and Moderna COVID-19 vaccines use messenger RNA (mRNA) technology. These vaccines contain small pieces of genetic material (called mRNA) that teach your cells how to make the SARS-CoV-2 spike protein. As a result, your immune system learns to release antibodies against the real virus if you’re exposed to it later on. Although the mRNA COVID vaccines are the first of their kind, mRNA vaccines were built from decades of research.
A relatively new respiratory syncytial virus (RSV) vaccine, called mRESVIA, also uses mRNA technology. It was first approved in May 2024.
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References
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