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COVID-19 Vaccines safety

19 February 2021 | Q&A

How do we know that COVID-19 vaccines are safe?

There are strict protections in place to help ensure the safety of all COVID-19 vaccines. Before receiving validation from WHO and national regulatory agencies, COVID-19 vaccines must undergo rigorous testing in clinical trials to prove that they meet internationally agreed benchmarks for safety and effectiveness.

Unprecedented scientific collaborations have allowed COVID-19 vaccine research, development, and authorizations to be completed in record time – to meet the urgent need for COVID-19 vaccines while maintaining high safety standards. As with all vaccines, WHO and regulatory authorities will continuously monitor the use of COVID-19 vaccines to confirm that they remain safe for all who receive them.


What are the side effects of COVID-19 vaccines?

Like any vaccine, COVID-19 vaccines can cause mild side effects, such as a low-grade fever or pain or redness at the injection site. Most reactions to vaccines are mild and go away within a few days on their own. More serious or long-lasting side effects to vaccines are possible but extremely rare. Vaccines are continually monitored to detect rare adverse events. 

Reported side effects to COVID-19 vaccines have mostly been mild to moderate and short-lasting. They include: fever, fatigue, headache, muscle pain, chills, diarrhoea, and pain at the injection site. The chances of any of these side effects following vaccination differ according to the specific COVID-19 vaccine.


What is the link between COVID-19 vaccines and allergic reactions?

WHO is aware of reports of severe allergic reactions in a small number of people who received a COVID-19 vaccine. A severe allergic reaction – such as anaphylaxis – is a potential but rare side effect with any vaccine. In persons with a known risk, such as previous experience of an allergic reaction to a previous dose of the vaccine or any of the known components in the vaccine, precautions may need to be taken.

WHO recommends that healthcare providers assess patient medical history to determine if a patient is at risk for severe allergic reaction to a COVID-19 vaccine. All immunization providers should be trained to recognize severe allergic reactions and take practical steps to treat such reactions if they occur. 

COVID-19 vaccine use will be closely monitored by national authorities and international bodies, including WHO, to detect serious side effects, including any unexpected side effects. This will help us better understand and manage the specific risks of allergic reactions or other serious side effects to COVID-19 vaccines that may not have been detected during clinical trials, ensuring safe vaccination for all.


What happens if an adverse event is reported?

As with any vaccine, it is essential to closely monitor the safety and efficacy of COVID-19 vaccines as they are delivered. If a problem is reported following vaccination, a thorough investigation should take place.

During these investigations, it is extremely rare that health problems are found to be caused by the vaccine itself. Adverse events are most often found to be coincidental and may be entirely unrelated to vaccination. Sometimes they are related to how the vaccine has been stored, transported, or administered. Such errors can be prevented by better training health workers and strengthening supply chains.

In the very rare cases where a genuine adverse reaction is suspected, the vaccine may be suspended from use. Further investigations will take place to determine what exactly caused the event, and corrective measures will be put in place. WHO works with vaccine manufacturers, health officials and other partners to monitor any safety concerns and potential side effects on an ongoing basis.


Under what circumstances should a COVID-19 vaccine be recalled?

Vaccine recalls or withdrawals due to safety issues are rare. Recalls are usually initiated voluntarily by a vaccine manufacturer before any adverse events are reported. For example, ongoing monitoring of vaccine production may show that an irregularity has caused a batch of vaccines to lose their strength. In this case, people who have received a vaccine from that batch may need to be vaccinated again to ensure they are protected.


How will WHO inform the public about suspected or confirmed adverse events related to COVID-19 vaccines?

Suspected safety events officially reported to WHO go through a series of rapid verification steps involving an independent panel of experts. WHO shares the results of these evaluations on its website.

WHO also coordinates with local, regional, and national health officials to investigate vaccine safety concerns and advise on next steps. Information is also made available through the Vaccine Safety Net, a publicly available network of digital international resources on vaccine safety that have been approved by WHO.


Is it possible that someone vaccinated against COVID-19 will still get infected?

While several COVID-19 vaccines appear to have high levels of efficacy, no vaccine is 100% protective. As a result, there may be a small percentage of people who do not develop protection as expected after COVID-19 vaccination.

In addition to a vaccine's specific characteristics, several factors such as a person's age, their underlying health conditions or previous exposure to COVID-19 may have an impact on a vaccine’s effectiveness. We also do not yet know how long immunity from different COVID-19 vaccines will last. That is one reason why, even as COVID-19 vaccines start to be rolled out, we must continue using all public health measures that work, such as physical distancing, masks, and handwashing.


Who should be excluded from receiving COVID-19 vaccines?

Medical professionals can best advise individuals on whether or not they should receive a COVID-19 vaccine. However, based on available evidence, people with the following health conditions should generally be excluded from COVID-19 vaccination in order to avoid possible adverse effects:

  • If you have a history of severe allergic reactions to any ingredients of the COVID-19 vaccine
  • If you are currently sick or experiencing symptoms of COVID-19, though you can get vaccinated once your primary symptoms have resolved.

Further research is needed to determine the safety and efficacy of different COVID-19 vaccines in certain population groups. In addition to the general recommendations above, each vaccine may have specific considerations for specific populations and health conditions.


Is it safe for pregnant women, those planning to become pregnant, and breastfeeding mothers to receive COVID-19 vaccines?

Based on what we know about these vaccines, we don’t have any specific reason to believe there will be risks that would outweigh the benefits of vaccination for pregnant women. While pregnancy puts women at higher risk of severe COVID-19, very little data are available to assess vaccine safety in pregnancy.  

For this reason, those pregnant women at high risk of exposure to SARS-CoV-2 (e.g., health workers) or who have comorbidities which add to their risk of severe disease may be vaccinated in consultation with their health care provider.

It is not yet clear whether COVID-19 vaccines can be excreted through breastfeeding. To determine the best course of action, the developmental and health benefits of breastfeeding should be considered along with the mother’s clinical need for immunization against COVID-19. WHO does not recommend discontinuing breastfeeding after vaccination.


Are mRNA vaccines safe? If they’re based on new technology, how can we be sure?

The COVID-19 mRNA vaccine technology has been rigorously assessed for safety, and clinical trials have shown that mRNA vaccines provide a long-lasting immune response. mRNA vaccine technology has been studied for several decades, including in the contexts of Zika, rabies, and influenza vaccines. mRNA vaccines are not live virus vaccines and do not interfere with human DNA.


How will WHO ensure vaccine safety monitoring and response when COVID-19 vaccines are used?

Vaccine safety monitoring is ensured at the national, regional, and global level. As is standard practice in all national immunization programmes, WHO supports the set up of safety monitoring systems for COVID-19 vaccines in every country. After a COVID-19 vaccine is introduced in a country, WHO works with vaccine manufacturers, health officials and other partners to track safety concerns and potential side effects on an ongoing basis. Specific safety concerns that may arise will be evaluated by WHO and an independent group of experts (the Global Advisory Committee on Vaccine Safety, or GACVS) in conjunction with the relevant national authorities.