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What are mRNA vaccines and how do they work?
What are mRNA vaccines and how do they work?
An mRNA vaccine is a shot that teaches your body to recognise a disease. It does not contain a live virus. It contains a short message: mRNA.
mRNA means messenger RNA. Your body makes mRNA all day. That message tells a cell which protein to make.
In an mRNA vaccine, the message is made in a lab. It is about one harmless piece of the virus. For COVID-19, that is often the spike protein. Then your body clears the message quickly.
The World Health Organization (WHO) calls this a vaccine with a blueprint, instead of the virus itself.
How does an mRNA vaccine work, step by step?
According to the US CDC, it works like this:
- You get the shot in the upper arm.
- The mRNA sits in tiny fat bubbles. Those help the message enter the cell.
- Inside the cell, the body reads the message and makes a harmless protein piece.
- Then the cell breaks the mRNA down. It leaves the body as waste.
- The cell shows the protein piece to your immune system.
- Your immune system makes antibodies and memory cells.
- If you later meet the real virus, your body recognises it faster.
The CDC says it usually takes a few weeks for that protection to be ready.
Does an mRNA vaccine change your DNA?
No. The CDC and the European Medicines Agency (EMA) both say this.
The mRNA does not enter the cell nucleus. That is where your DNA is. The message stays outside the nucleus, where your body always makes proteins.
mRNA is also chemically different from DNA. It cannot simply sit inside your DNA.
The EMA also says an mRNA vaccine is not gene therapy. The aim is not to repair or change your genes.
The vaccine cannot give you COVID-19. There is no live coronavirus in it, says the CDC.
How long does the mRNA stay in your body?
Not long. The EMA says the body breaks the mRNA down quickly, just like your own mRNA.
In animal studies of Comirnaty (Pfizer/BioNTech), mRNA levels fell over 6 to 9 days. For Spikevax (Moderna), researchers found after 1 to 3 days that remaining mRNA was mainly at the injection site, in lymph nodes and in the spleen.
At approval, regulators did not expect a build-up in organs.
Why are there fat bubbles in the vaccine?
mRNA is fragile. Without protection it falls apart quickly.
The EMA explains: tiny fat particles, lipid nanoparticles, help the mRNA enter the cell. The cell wall is also made of fat. The bubbles fuse with it.
This kind of fat particle in medicines is not new. The first medicine with these bubbles was authorised in the EU in 2018.
Are mRNA vaccines new?
COVID-19 shots were new for many people. The technology was not.
The EMA says researchers had already worked with mRNA for about twenty years, for infectious diseases and for cancer. The CDC mentions earlier studies for flu, Zika, rabies and CMV.
mRNA is relatively small and simple to make. That is why manufacturers could scale up faster than with classic vaccines. Safety tests were not skipped, says the CDC.
Which mRNA vaccines exist?
The best known in Europe are:
- Comirnaty from Pfizer/BioNTech
- Spikevax from Moderna
They are authorised by the EMA. The Dutch institute RIVM uses COVID-19 vaccines in its autumn programme, mainly for people at higher risk. In 2026, people aged 70 and over, and people with extra medical risk, can get a COVID-19 shot.
There are also other types of COVID-19 vaccines, such as protein vaccines. Those already contain a protein piece. RIVM says that can be an option if you cannot or do not want an mRNA vaccine for medical reasons.
The RIVM guideline puts it simply: Comirnaty is an mRNA vaccine. It contains no live virus. The mRNA codes for the spike protein.
mRNA is also being studied for other diseases, and for some cancers. That is still research. A COVID-19 mRNA vaccine is not the same as a personal cancer vaccine.
What are the side effects?
The WHO says mild to moderate symptoms can happen. That is a sign your body is building protection.
Common ones:
- pain or redness at the injection site
- tiredness
- headache
- muscle ache
- chills
- fever
Most symptoms go away within a few days. Not everyone gets side effects.
Serious side effects are rare. The EMA says the safety of authorised COVID-19 vaccines is reassuring, after hundreds of millions of doses.
A known rare side effect of mRNA vaccines is inflammation of the heart muscle or the lining around the heart. Doctors call this myocarditis or pericarditis. RIVM calls this rare. It happens mostly in young men, shortly after the shot. Most people recover. See a doctor if you get chest pain, shortness of breath or a fast heartbeat after the shot.
Do mRNA vaccines still protect?
Yes, especially against severe disease and death. No vaccine works 100%.
The WHO says protection is highest in the first months. After about six months it starts to fall. That is why people at higher risk sometimes get another shot.
You can still get COVID-19 after vaccination. The chance of becoming very ill is then usually lower.
What does this mean for your vaccination record?
Write down which shot you had, the date, and the vaccine name, such as Comirnaty or Spikevax. That helps for a later dose, for travel, or if a doctor asks.
With Vaxy you keep those details in one place, for yourself and your family.
This article is information, not medical advice. If you are unsure, ask your doctor or local public health service.
Short answers
What is an mRNA vaccine? A shot with a short message for your cells. No live virus.
How does it work? Your cells make a harmless protein piece. Your immune system learns it. Then the mRNA disappears.
Does it change your DNA? No. The CDC and EMA say the mRNA does not reach your DNA in the cell nucleus.
Can you get COVID-19 from it? No. There is no live coronavirus in it.
How long does the mRNA stay in your body? Not long. The EMA says your body breaks it down quickly.
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