How do I know if a COVID-19 vaccine is safe?

It is important that COVID-19 vaccines are safe. Like any other vaccines, COVID-19 vaccines are also subject to strict standards for safety and side effects. A COVID-19 vaccine cannot be used until the application for marketing authorisation has been approved. At the European level, the safety, efficacy and quality of medicinal products – including vaccines – are assessed by the European Medicines Agency (EMA). In the Netherlands, the Dutch government is also involved in assessing medicinal products through the Medicines Evaluation Board (CBG-MEB). Before a vaccine is approved, its benefits (protection against disease) must be assessed in relation to its drawbacks (possible side effects). If a vaccine receives a positive opinion in this initial assessment, a marketing authorisation will be granted by the European Commission which is then valid in all EU European Union (European Union) member states. No vaccines are used that have not been assessed and subsequently approved by the EMA for use in Europe. 

Ongoing monitoring of vaccine safety

Hundreds of millions of people worldwide have already been vaccinated using mRNA vaccines, and a great deal of information is already known about the side effects. At the same time, the safety of COVID-19 vaccines continues to be monitored. In the Netherlands, the Pharmacovigilance Centre Lareb collects, registers and investigates reports of possible side effects. 

Even after vaccines are approved, they continue to be monitored by the EMA and CBG-MEB to assess how well they work and identify possible side effects.  Monitoring takes place based in part on data from the Pharmacovigilance Centre Lareb. EudraVigilance is a system that allows the EMA and EU member states to continuously collect, monitor and investigate reports of suspected side effects, regarding vaccines in clinical trials and registered vaccines. If research shows that a vaccine does indeed cause a suspected side effect, this is then included in the vaccine’s product information.  

Can an mRNA vaccine against COVID-19 change your DNA?

No. DNA is located in the cell nucleus of the body’s cells. The mRNA in the COVID-19 vaccine cannot enter into the cell nucleus, so it remains outside the nucleus, in the cell’s cytoplasm. The mRNA in the COVID-19 vaccination cannot replicate (make copies of itself), and it cannot penetrate the cell nucleus because the necessary enzymes for that are not present. In other words, mRNA vaccines cannot alter your cell DNA because they are unable to access the place where the DNA is located. 

What does the mRNA in the COVID-19 vaccine do? 

The mRNA in a COVID-19 vaccine is a small fragment of genetic code from the coronavirus SARS-CoV-2 that is coded for making spike protein.  These proteins are the spiky protrusions on the exterior of the coronavirus; it is possible to make antibodies that respond to the presence of the spike proteins. The mRNA is encapsulated in a lipid envelope (fat globule) that merges with the cells of your body located around the injection site in your upper arm where you get the COVID-19 vaccination. When that happens, the mRNA is released into the cell, causing these body cells to produce spike proteins. The vaccine does not contain the whole virus, only a fragment of mRNA that makes spike protein in the cell cytoplasm (inside the cell, outside the nucleus). You cannot get COVID-19 from this, but your immune system does respond to the presence of these proteins. The immune system recognises the spike proteins as foreign substances and starts making antibodies and activating other parts of your immune system, like producing T-cells. This helps you build up protection against the coronavirus SARS-CoV-2, so your body responds quickly if and when you actually come into contact with the virus. 

Could there be DNA present in mRNA vaccines? 

The mRNA in a COVID-19 vaccine is made using plasmid DNA. Plasmid DNA is a separate fragment of circular DNA that can be produced in large quantities by single-celled organisms such as bacteria. In the production process for making COVID-19 vaccines, this plasmid DNA contains the correct code for making the mRNA, which in turn codes for the spike protein. It is not the same as DNA in chromosomes, which store an organism’s genetic material. 

Once the mRNA for the vaccine is produced, the plasmid DNA is no longer needed, so it is broken down and removed. The production and purification process is carefully controlled to ensure that plasmid DNA is removed from the product. Despite that, very small trace amounts of plasmid DNA may remain behind. The EMA has set limits on the permissible content of residual plasmid DNA fragments in mRNA vaccines. Vaccine manufacturers are required to measure various factors, including the levels of residual DNA in each batch of the active ingredient. These results are then rechecked by an official control laboratory. See also the EMA website. If the residual levels of plasmid DNA are too high in any specific batch, that batch is rejected and destroyed. 
The EMA monitors the safety of COVID-19 vaccines and has found no evidence of (serious) side effects resulting from any trace residues of DNA fragments in mRNA vaccines.

Can the DNA in mRNA vaccines change human DNA? 

The plasmid DNA fragments that may remain in the vaccine in very small quantities cannot penetrate into the nucleus of the cells in our bodies. This is partly due to the presence of a protective layer around your cell nucleus and partly due to the lack of the enzymes that would be needed to pass through that protective layer. 

What are the side effects of the mRNA vaccine that will be given in autumn 2024? 

The official package leaflet of the COVID-19 vaccine made by Pfizer/BioNTech can be found on the CBG-MEB website (in Dutch) and on the EMA website. The most common side effects after a COVID-19 vaccination usually go away within a day or two. They are often not serious, but can be annoying. Examples: muscle aches, swelling and pain at the injection site. These side effects occur because your body is making antibodies against the spike proteins of the coronavirus SARS-CoV-2. In very rare cases, a person may also have a serious side effect, such as myocarditis or pericarditis (inflammation of the heart muscle or outer lining of the heart), or an allergic reaction. The benefits of the COVID-19 vaccination (protection against serious illness) should outweigh the disadvantages (risk of serious side effects). In its latest advisory opinion on COVID-19 vaccination in 2024, the Health Council of the Netherlands indicated that the benefits of offering a seasonal autumn vaccination to over-60s, medical risk groups and care workers who have direct contact with vulnerable patients outweigh the minor risks of side effects.

The Pharmacovigilance Centre Lareb also has more information about side effects of the COVID-19 vaccines (in Dutch).

After a COVID-19 vaccination, could I still get inflammation of the heart muscle or outer lining of the heart?

In very rare cases, inflammatory diseases of the heart may occur following vaccination against COVID-19 with the mRNA vaccine made by Pfizer/BioNTech: myocarditis (inflammation of the heart muscle) or pericarditis (inflammation of the outer lining of the heart). These very rare side effects are seen most often in young men aged 16 to 24 years old. Studies show that myocarditis and pericarditis occurred most often within 7 days of the second vaccine dose in the basic series of COVID-19 vaccinations with an mRNA vaccine. 

Since mid-2023, one (annual) COVID-19 vaccination is advised for people in medical risk groups who could become seriously ill from COVID-19, and for care workers who have direct contact with vulnerable patients. There may still be a minor risk of myocarditis and pericarditis after COVID-19 vaccination, mainly among young men. 

But myocarditis and pericarditis are also a known risk of COVID-19 itself. And the symptoms are generally milder after vaccination than after infection.  
Symptoms of myocarditis (inflammation of the heart muscle) or pericarditis (inflammation of the outer lining of the heart):

• shortness of breath;
• chest pain;
• a forceful heartbeat that may sometimes be irregular.  

The symptoms can vary significantly in severity and usually improve on their own or can be treated effectively with medication. If you have these symptoms after vaccination, please contact your GP or treating physician and report them to Lareb.

Can the COVID-19 vaccination disrupt menstruation?

After COVID-19 vaccination, your menstrual period may temporarily be mildly to moderately disrupted. For example, you may notice changes in your cycle length, amount of bleeding, duration of menstruation, premenstrual and menstrual pain and spotting at other points in your cycle. Menstrual disorders have previously been seen as a side effect with other vaccines as well. A vaccine activates your immune system, which can affect your hormone levels or the build-up and breakdown of your endometrium (uterine lining). For more information, see the Lareb website. PRAC, the pharmacovigilance committee at the EMA, has been investigating menstrual disorders after the COVID-19 vaccination. The side effect was added to the package leaflet for Pfizer/BioNTech’s COVID-19 vaccine in 2022, but there is no evidence that menstrual changes that occur in some people after vaccination could affect fertility. See the EMA safety update(PDF). 

Can the COVID-19 vaccination make me infertile?

No. There are no adverse effects on fertility after the COVID-19 vaccination. Are you a care worker, or are you in the group that gets the seasonal flu vaccine annually? Then you can be vaccinated safely, even if you are pregnant or trying to become pregnant. Research shows that COVID-19 vaccination does not lead to functional changes in the vesicular follicle or blastocyst. Similarly, there is no evidence that the antibodies built up after vaccination react with a protein (syncytin-1) involved in placental development. See also the Lareb page about COVID-19 vaccination and pregnancy (in Dutch).