What Is a Messenger RNA (mRNA) Vaccine, and How Does It Differ From Other Vaccines?

Sarah Gupta, MD, is a board-certified physician with a special interest in anxiety, depression, sleep, and the human microbiome.

Key takeaways:

COVID-19 continues to cause illness, hospitalizations, and deaths around the world. Fortunately, vaccination against COVID-19 is already underway in the U.S. (follow our live updates here). 

As COVID-19 vaccines begin to roll out, attention has focused on the two leading vaccines, made by Pfizer-BioNTech and Moderna. Both of these vaccines use a brand-new technology called messenger RNA (mRNA), which means these types of vaccine have never been used before. If you have questions about mRNA vaccines, you’re not alone. You may wonder:

If you’re looking for answers, read on. We’ll help you understand what mRNA is, how it works in the body, and how COVID-19 mRNA vaccines can protect you from getting sick. 

What is mRNA?

Messenger RNA (mRNA) is a type of small molecule that your cells use to make protein. Each piece of mRNA is a unique set of instructions. It tells your cells how to assemble a specific protein by putting together building blocks (called amino acids) in a certain order. Your cells make and use mRNA molecules to make proteins every day. Proteins are essential to the structure and function of the human body.

Some of the new COVID-19 vaccines being developed contain mRNA. And just like the mRNA molecules your body already makes, the mRNA in COVID-19 vaccines tells your body how to make protein. In this case, vaccine mRNA contains the instructions for making a coronavirus “spike protein,” a surface protein on the virus that causes COVID-19. 

What is an mRNA vaccine and how does it differ from other vaccines?

A vaccine teaches your immune system how to recognize an invader that could make you sick, like influenza or the coronavirus that causes COVID-19. It does this by imitating an infection in your body, so your body can practice recognizing a virus and fighting it off. In some ways, a vaccine is like a training exercise for your immune system. 

Most vaccines — like the flu shot — are made from dead or inactivated virus parts. When you get vaccinated, these harmless virus parts are injected into your body. This helps your immune system learn to recognize the virus, without the risk of getting sick. 

After you are vaccinated, your body begins to make antibodies. These are special proteins that help your body fight off a virus. Your immune system remembers how to make these antibodies for months or even years (depending on the vaccine). This can keep you from getting sick if you are exposed to the virus in the future. 

The mRNA COVID-19 vaccines do the same job: They teach your body to recognize a virus and protect you from getting sick. But mRNA vaccines work differently. They do not contain dead or inactive virus parts. Instead, they contain small molecules called mRNA — instructions for making a harmless part of the coronavirus inside your own cells. This does not give you the coronavirus. 

When you are vaccinated, mRNA is injected into your body and enters your cells. Your cells use the mRNA to make the part of the coronavirus that causes COVID-19. Just like with other vaccines, your immune system responds by making antibodies. These antibodies will help to protect you if you are exposed to the real virus that causes COVID-19. 

How are traditional vaccines made?

Traditional vaccines are very effective, but they can be time consuming to make. This is because most vaccines start with a live version of the virus, which has to be killed or inactivated before it can be injected into your body. Growing the virus and making it safe to be injected into your body takes a lot of time. 

For example, the annual influenza vaccine (flu shot) takes over 6 months to make. The flu viruses are often grown in a lab, then in chicken eggs. The viruses then have to be harvested, killed, and purified — and then distributed to clinics and pharmacies around the country. 

How are mRNA vaccines made?

Messenger RNA vaccines can be made faster than traditional vaccines. This is partly because part of the production happens in your body — after you are vaccinated — when your own cells build the virus protein. This means vaccine makers don’t have to grow, purify, and inactivate the virus separately. 

Also, mRNA molecules are simpler structures than viruses. This means that they can be made easily in a lab, using readily available materials. This also makes mRNA vaccines faster to produce. 

One challenge is that mRNA is fragile. The mRNA has to be put inside a lipid (fat) coating for protection. Because this lipid coating can melt at room temperature, mRNA vaccines have to be kept very cold during transport and storage. For example, the Pfizer-BioNTech mRNA COVID-19 vaccine is stored at -94°F (-70°C) — much colder than other vaccines that often only need to be refrigerated.

How was mRNA vaccine technology discovered?

Though COVID-19 mRNA vaccines are the first of their type, mRNA technology is not entirely new. For decades, scientists have been interested in using custom-made mRNA vaccines and treatments. One of the biggest challenges in the past was how to transfer mRNA into body cells. In 2005, scientists figured out how to put mRNA in a stable package and safely deliver it to the cells. 

This previous research — combined with worldwide collaboration — has made it possible for scientists to develop mRNA COVID-19 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 vaccine.

Which COVID-19 vaccines are mRNA vaccines?

There are currently two mRNA vaccines: Pfizer-BioNTech and Moderna. Both of these vaccines require 2 doses to be effective. 

The Pfizer-BioNTech vaccine was approved earlier this month for emergency use in the U.S, U.K., and Canada. Shortly after, Moderna’s vaccine became the second to receive emergency use approval in the U.S. Follow our live updates for details on which vaccines are currently approved for use in the U.S. 

Are mRNA vaccines safe?

Yes. According to the Centers for Disease Control and Prevention (CDC), mRNA COVID-19 vaccines have been thoroughly tested for safety before being approved for use in the U.S. All COVID-19 vaccines are held to the same rigorous safety standards as all other vaccines used in the U.S.

Though some people may have side effects, you cannot get COVID-19 from a vaccine. This is medically impossible. Messenger RNA vaccines are not a live virus. They only contain a small bit of genetic information about the virus that causes COVID-19.

It’s also good to note that mRNA vaccines cannot change your body’s own DNA. Messenger RNA from the COVID-19 vaccines never enters the part of the cell where your DNA lives (the cell nucleus). In fact, mRNA doesn’t interact with your DNA at all. And mRNA doesn’t even hang around for very long — it’s broken down right after it helps your cells make the spike protein. 

Not only are mRNA vaccines safe, they may potentially work better than traditional vaccines. This is because mRNA vaccines may stimulate your immune system in two different ways — to make antibodies and to make immune system “killer” cells. This could potentially make your immune system even more prepared to protect you from COVID-19. More research is needed to understand how mRNA vaccines compare. 

Do any other licensed vaccines or therapeutics use mRNA technology?

No. This is the first time that mRNA has been licensed for use for any disease. But researchers have been studying and working with mRNA vaccines for decades. They have been previously studied for other viruses, including flu and Zika. Messenger RNA has also been researched as a cancer treatment, to help people’s immune systems recognize certain cancer-related proteins.

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