COVID-19 vaccines: key facts
The European Medicines Agency (EMA) continues to monitor the safety of vaccines against COVID-19 and to ensure that they offer protection in the European Union (EU), even though the public health emergency has ended. On this page you can find answers to key questions on the effectiveness and safety of COVID-19 vaccines in general, as well as on mRNA vaccines in particular.
The COVID-19 vaccines authorised in the EU continue to prevent severe disease, hospitalisation and death linked to COVID-19.
The SARS-CoV-2 virus keeps changing, as viruses do when they spread among people over time. When the virus becomes significantly different from the original virus, it is known as a variant. Therefore, the vaccines need to be routinely updated to target future virus variants and broaden immunity.
COVID-19 vaccines are routinely updated in the same manner as flu (influenza) vaccines.
Flu vaccines are adapted every year in response to emerging virus variants. This ensures people remain protected over time, in particular vulnerable groups.
EMA expects future COVID-19 vaccination campaigns to take place once per year in the EU using updated COVID-19 vaccines, at the start of the cold season.
For more information, see:
Update: The main aim of any vaccine is to protect people against a disease. COVID-19 vaccines are authorised for preventing COVID-19.
This does not necessarily mean that the vaccines cannot reduce virus transmission or be used with the additional aim of reducing transmission.
It is difficult to measure how well vaccines may reduce transmission in clinical studies. This can only be done in real-world studies that include large numbers of vaccinated people.
At the beginning of the pandemic, regulators asked companies to prioritise studies looking at how well the vaccines prevented severe disease and death. Regulators did not ask companies to look at the effects of their vaccines on transmission as part of their request for authorisation.
Several studies carried out after authorisation have shown that COVID-19 vaccines can reduce the transmission of the virus.
The effectiveness of COVID-19 vaccines in preventing transmission varies over time and between countries. These variations depend on the virus strains in circulation, and other measures put in place to reduce transmission.
- Decreased infectivity following BNT162b2 vaccination: A prospective cohort study in Israel - The Lancet Regional Health – Europe
- Vaccination with BNT162b2 reduces transmission of SARS-CoV-2 to household contacts in Israel | Science
- Infectiousness of SARS-CoV-2 breakthrough infections and reinfections during the Omicron wave | Nature Medicine
- Indirect Protection by Reducing Transmission: Ending the Pandemic With Severe Acute Respiratory Syndrome Coronavirus 2 Vaccination | Open Forum Infectious Diseases | Oxford Academic (oup.com)
- Vaccine effectiveness against transmission of alpha, delta and omicron SARS-COV-2-infection, Belgian contact tracing, 2021–2022 - PMC (nih.gov)
- Effect of SARS-CoV-2 prior infection and mRNA vaccination on contagiousness and susceptibility to infection | Nature Communications
- Effect of COVID-19 vaccination on household transmission of SARS-CoV-2 in the Omicron era: The Vaccine Effectiveness, Networking, and Universal Safety (VENUS) study - International Journal of Infectious Diseases (ijidonline.com)
The World Health Organization (WHO) declared the end of the emergency phase of the pandemic in May 2023.
However, WHO highlighted that COVID-19 remains a health threat.
New virus variants can potentially still escape the body's immune system and cause infections, serious disease and even death.
COVID-19 still places a burden on healthcare systems and individual people whose immunity has decreased with time.
In the EU, national authorities in the EU Member States will decide who should be offered COVID-19 vaccination and when, taking account of infection rates, hospitalisation rates, risks to vulnerable people, vaccination coverage and other factors.
In the EU, each EU Member State is responsible for vaccination campaigns within its own territory.
Public health authorities in each EU country develop vaccination campaigns based on the spread of the virus and healthcare system capacity.
There may continue to be differences between how different EU countries use the COVID-19 vaccines at their disposal.
EMA’s evaluations provide a scientific basis for national vaccination campaigns. They describe the benefit-risk balance of each vaccine in the different populations studied.
The benefits of all authorised COVID-19 vaccines outweigh the risks when used as described in the product information.
COVID-19 vaccination is estimated to have saved millions of lives in the EU and beyond.
Researchers have estimated that the first year of COVID-19 vaccination more than halved the number of deaths due to COVID-19 across the world, avoiding between 14 and 20 million deaths.
In May 2022, WHO estimated there were nearly 15 million excess deaths linked to the pandemic in 2020 and 2021 alone.
Widespread vaccination also allowed the lifting of lockdowns and eased the pressure on healthcare systems, by protecting people against severe disease and hospitalisation.
For more information, see:
A full list of side effects associated with each COVID-19 vaccine is found in the vaccine's product information.
EMA and the EU Member States continuously monitor reports of suspected side effects with COVID-19 vaccines. This serves to detect any new safety issues.
Suspected side effects are medical events reported after vaccination by a vaccinated person or their healthcare professional. They are collected in the EU database of suspected side effects, EudraVigilance, and are available in a public database - adrreports.eu.
The fact that a medical event was reported as a suspected side effect does not mean that the vaccine caused it.
When assessing the data, EMA and EU Member States look for any unusual or unexpected patterns, such as a medical event occurring more often in vaccinated people than in the general population. Regulators take into account every single report in EudraVigilance, regardless of how much time has passed between receiving the vaccine and the occurrence of the event.
They also consider other sources of evidence, such as studies and the medical literature.
If there is at least a reasonable possibility that a vaccine could have caused a suspected side effect, this is included in the vaccine’s product information.
The product information also indicates the likelihood of the side effect occurring and how to reduce the risk.
For more information, see:
- Safety of COVID-19 vaccines
- EudraVigilance - European database of suspected adverse drug reaction reports
EMA carefully reviews all safety data and can confirm that there is no evidence of an increase in deaths related to COVID-19 vaccination in any age group.
Data published by Eurostat have shown increased numbers of excess deaths in many EU countries over the past years. This largely coincided with waves of increased COVID-19 infections.
The medical literature shows that infection with SARS-CoV-2 can lead to serious health problems, such as heart attack and stroke, even several weeks or months after infection.
Evidence gathered from hundreds of millions of vaccinated people confirms that the safety profile of COVID-19 vaccines authorised in the EU is very reassuring.
The vast majority of known side effects are mild and short-lived. Serious side effects may occur, but they are very rare.
Reports of deaths following vaccination are very rare.
During mass vaccination campaigns, it is expected that some deaths will occur shortly after vaccination. This does not mean the vaccine caused the death.
Healthcare professionals can report any death that occurs following vaccination, even if it is unknown if the vaccine was the cause.
In very exceptional cases, deaths have been confirmed to be caused by a vaccine.
COVID-19 vaccines have been used in hundreds of millions of people around the world and are subject to intensive safety monitoring.
Long-term safety data on COVID-19 vaccines are very reassuring.
Data are available from studies in thousands of volunteers and from mass vaccination campaigns across the world over more than two years.
Moreover, safety monitoring of vaccines shows that any side effect usually occurs within two months of vaccination.
EMA and the EU Member States will continue to closely monitor the safety of COVID-19 vaccines in the long term.
Scientific evidence increasingly shows that infection with SARS-CoV-2 can lead to a wide range of long-term symptoms, referred to as long COVID.
This can also happen in young people.
Symptoms include long-term organ damage, which can even lead to death several weeks or months after the initial acute infection.
There is increasing evidence that vaccinated people who become infected with SARS-CoV-2 are less likely to report symptoms of long COVID than unvaccinated people, but more evidence is needed to establish the size of this effect.
Several studies have shown that messenger RNA (mRNA) COVID-19 vaccines do not cause complications in pregnancy, either for expectant mothers or their babies.
On the contrary, COVID-19 vaccines protect expectant mothers and their babies.
The studies did not show any sign that the COVID-19 vaccines increased the risk of complications in pregnancy, miscarriage, premature birth or harm to the unborn baby.
The data also confirmed that the vaccines reduced the risk of hospitalisation and death for pregnant people as much as for other people.
Side effects in pregnant people are similar to those in other vaccinated people. They are mostly mild or moderate and resolve within a few days.
Meanwhile, people infected with SARS-CoV-2 during pregnancy are particularly likely to become severely ill with COVID-19, especially in the second and third trimesters.
Data from many thousands of people who received an mRNA vaccine while breastfeeding found no risk of side effects in breastfed babies.
Recent research has found tiny amounts of vaccine mRNA in breast milk during the first 48 hours after vaccination, but not afterwards.
Although more work is needed to understand the relevance of these findings, this amount of mRNA is very small and is not expected to cause any safety problem.
There is also evidence that breastfeeding people who received an mRNA vaccine have antibodies against the SARS-CoV-2 virus in their breastmilk, which may help to protect their baby against infection.
COVID-19 vaccines are well tolerated in children, based on data from millions of children who have been vaccinated.
The side effects are usually mild or moderate and go away in a few days, based on real-world evidence and clinical trials in children.
Very rare cases of myocarditis and pericarditis (inflammatory conditions affecting the heart) have occurred in adolescents and adults after vaccination with certain COVID-19 vaccines. This risk is much lower in children aged 5 to 11 years.
These conditions usually clear up following treatment, as they do when unrelated to vaccination (for instance, as a result of a COVID-19 infection).
EMA continues to monitor data on safety in children in the long term.
The technology used to develop the mRNA COVID-19 vaccines had already been extensively studied for some twenty years in the prevention of other infectious diseases and in cancer treatment.
A wealth of scientific knowledge about viruses of the same family as SARS-CoV-2 also helped accelerate vaccine development.
mRNA is a relatively small and simple molecule that is much easier to produce than more traditional vaccines. This means that producing mRNA vaccines for clinical trials, and then scaling up production for mass vaccination campaigns was faster than previously possible with other technologies.
Lipid nanoparticles are small fat particles used in mRNA vaccines to help the mRNA enter human cells.
Once the vaccine is injected into the muscle, the lipid nanoparticles fuse with the cell membrane which is also made up of lipids (fats).
This mainly happens in immune cells found around the injection site.
The immune cells that contain the lipid nanoparticles and the mRNA then move to nearby lymph nodes, where they stimulate an immune response.
Lipid nanoparticles are also important in maintaining the quality of the vaccine during storage, for example by keeping the vaccine stable and making sure the vaccine components work properly.
The use of lipid nanoparticles in medicines has been researched extensively. The first medicine using lipid nanoparticles was authorised in the EU in 2018.
Messenger RNA (mRNA) is a type of molecule that exists naturally in the body and helps make proteins.
The cells in the body translate the information in the mRNA molecule to produce specific proteins.
Animal studies for Comirnaty, in which much higher doses of mRNA were used than in the final vaccine given to people, found that the mRNA and lipid nanoparticles stayed mainly at the injection site and lymph nodes where they are able to stimulate the immune response.
In these cases, only small amounts of mRNA were shown to reach other tissues, mainly the liver but also the spleen, heart, kidney, lung and brain.
Levels of mRNA decreased over 6 to 9 days after injection, just like mRNA produced by the body.
For Spikevax (previously COVID-19 Vaccine Moderna), animal studies were carried out using an mRNA vaccine that is similar to Spikevax.
The results only detected small amounts of mRNA in tissues beyond the injection site. After 1 to 3 days, the mRNA was found only at the injection site, the lymph nodes and the spleen. Based on these findings, at the time of authorisation, no build-up of mRNA or lipid nanoparticles in the organs was expected.
Since then, hundreds of millions of people have used the mRNA COVID-19 vaccines throughout the world. Intensive safety monitoring of COVID-19 vaccines has not detected any safety issue linked to the distribution of these vaccines in the human body.
Like all mRNA molecules, the mRNA in the COVID-19 vaccines is broken down by cell mechanisms and so spends a relatively short time in the body.
Animal studies in Comirnaty found that only small amounts of mRNA reached tissues beyond the lymph nodes, and the levels decreased over 6 to 9 days after injection.
More recently, a study in vaccinated people suggested that mRNA and the spike protein produced are rapidly removed from the bloodstream but may stay longer in the lymph nodes. This is to be expected, as this is where the immune response starts.
The companies marketing mRNA COVID-19 vaccines are carrying out more animal and laboratory studies to obtain additional data on how mRNA and the spike protein are distributed and broken down in the body. They will submit the results to EMA for assessment.
The mRNA in Comirnaty and Spikevax is manufactured using plasmid DNA.
Plasmids occur naturally in bacterial cells. They are used as a template to produce the mRNA of the vaccines.
Once the mRNA is produced, the manufacturing process includes steps to break down and remove the plasmid DNA as it is no longer needed.
The plasmid DNA is not intended to be part of the final mRNA vaccines. However, very small amounts of DNA fragments may remain. EMA has seen no evidence linking the residual DNA to side effects.
EMA has set limits for the level of broken-down DNA in mRNA vaccines. The manufacturing process is carefully designed and controlled to ensure safe and acceptable levels, and the vaccines’ quality is routinely checked.
The mRNA used in COVID-19 vaccines does not interfere with our genetic code. This is because:
- mRNA does not enter the cell’s nucleus where our DNA is kept, but uses the cell’s machinery present outside the nucleus to make proteins, just like any other human mRNA;
- mRNA, in general, has a different chemical composition than DNA, and this prevents it from being able to directly integrate into a DNA strand.
Although mRNA can be converted into DNA, this can only be done with a specific enzyme called reverse transcriptase, which is not normally present in human cells, nor is it present in the vaccine.
No side effects linked to gene mutations, such as cancer, have been observed after vaccination with mRNA vaccines.
COVID-19 mRNA vaccines can sometimes contain truncated (shorter) or modified mRNA molecules. These are considered impurities and are not expected to affect safety or efficacy.
There is no evidence that truncated mRNA is translated into shorter or modified forms of the spike protein.
Human cells have several processes ensuring that proteins are correctly produced and preventing the production of shorter or modified proteins from faulty mRNA.
In the unlikely event that shorter or modified spike proteins were produced, they would not be expected to trigger unwanted immune responses.
Although the risk of producing shorter or modified spike proteins is low, this risk will continue to be monitored as part of the long-term safety monitoring.
- European Vaccination Information Portal
- European Commission: Safe COVID-19 vaccines for Europeans
- Council of the EU: COVID-19 vaccines: Why so fast?
- Council of the EU: mRNA vaccines: What gets injected into my body?
- The World Health Organization (WHO)
- European Centre for Disease Prevention and Control (ECDC)