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COVID-19 vaccine - Safety and effectiveness of COVID-19 vaccine

Are there any side effects for the COVID-19 vaccines?

Like all medicines, vaccines can cause side effects. Most side effects are mild and short-term, and not everyone gets them.

The most common side effects should only last a day or two, and include:  

  • a heavy feeling or soreness where you had the injection
  • general aches or mild flu-like symptoms
  • feeling sick or vomiting 
  • diarrhoea
  • tiredness
  • headache, and 
  • mild fever.  

Babies under two years old may also be irritable, sleepy and lose their appetite. 

You may have a mild fever for two to three days after having a vaccine. However, a high temperature is unusual and may be because you have another infection or illness. If you are worried, speak to your doctor or nurse.

You can take paracetamol (follow the advice in the packet and do not take more than the recommended dose), and rest to help you feel better. Children under 16 should not be given medicines that contain aspirin. 

 An uncommon side effect after the COVID-19 vaccine is swollen glands in the armpit or neck, on the same side as the arm where you had the vaccine. This can last for around 10 days, but if it lasts longer contact your GP surgery for advice. If you are due for breast screening (a mammogram) in the few weeks after the vaccine, mention you’ve had the COVID-19 vaccine when you attend. 

 Very rarely cases of inflammation of the heart have been reported after some COVID-19 vaccines. This is called myocarditis or pericarditis. These cases have been seen mostly in younger men within several days after vaccination. Most of these people recovered and felt better following rest and simple treatment.

You should get medical advice urgently if you have:

  • chest pain    
  • shortness of breath, or    
  • a fast-beating, fluttering, or pounding heart.  

Other side effects are uncommon or very rare.

If your symptoms seem to get worse or if you are concerned, call NHS 111 or your GP surgery. If you do get advice from a doctor or nurse, make sure you tell them what vaccines you have had so they can assess you fully. You can also go to the NHS 111 Wales website online.

Where can I find patient information leaflets?

For more information about the vaccine, including its contents and possible side effects, you can look at the patient information leaflet.  

A black triangle symbol on a vaccine or medicine means that it is being closely monitored for any side effects. This will allow quick identification of new safety information. You can help by reporting any side effects you or your child may get.

You should report any side effects of the vaccine through the Yellow Card scheme online, by downloading the Yellow Card app or calling 0800 731 6789 (Monday to Friday, 9am to 5pm).  

If I am unwell, should I have the vaccine?

If you are ill, it is best to wait until you are better to have the vaccine, but you should try to have it as soon as possible. If you cannot attend your vaccination appointment, please cancel and rearrange the appointment. A cold or other minor illness is not a reason to delay your vaccine. If in doubt, discuss this with the person giving you your vaccination. 

I had an allergic reaction to a previous dose of COVID-19 vaccine. Should I have further doses?

The British Society for Allergy and Clinical Immunology (BSACI) have given advice on allergic reactions. They have said that people who had a reaction to the first dose of a COVID-19 vaccine may be able to receive further doses.  

After a review by a specialist, many individuals have received subsequent doses of the same vaccine. This is preferred as it stops you being incorrectly labelled as allergic for life. 

The Anaphylaxis UK website also offers information to individuals with allergy.

There are very few people who should not have a COVID-19 vaccine. Most people with allergies can have the vaccine with no problems. The vaccine should not be given to anyone who has had a serious (life-threatening) reaction to:  

  • a previous dose of the vaccine, or 
  • any ingredient in the vaccine. 

Make sure you tell the person giving you the vaccine if you have had a serious allergic reaction to the vaccine or its ingredients in the past.

What if I have other allergies? Can I have the COVID-19 vaccine?

Yes. The current COVID-19 vaccines are safe for those with allergies (including anaphylaxis) to: 

  • wasp, bee, or other insect stings 
  • penicillin or other antibiotics 
  • nuts, or another food or drink. 

The nurse or person giving the vaccination will be able to discuss the vaccine at the appointment and answer any questions. 

Will the COVID-19 vaccine stop me from catching the virus?

Vaccination is one of the best ways to help prevent severe illness from COVID-19. It may take a few weeks for your body to build up protection against COVID-19 after the vaccination.

Like all medicines, no vaccine is 100% effective – some people may still get COVID-19 despite having a vaccination, but their symptoms should be less severe.

Your levels of protection may begin to reduce over time, so you may need to have additional vaccines.

The UK vaccination programme has been very successful, with millions of people vaccinated and thousands of lives saved. 

It is still important to know the signs and symptoms of COVID-19, even if you or your child are vaccinated. Get more guidance for people with symptoms of a respiratory infection, including COVID-19.

I am eligible to receive the COVID-19 vaccine, but I am pregnant or trying to become pregnant. Can I still have the vaccine?

Yes, all COVID-19 vaccines used in the UK can be given to eligible pregnant women, or those trying to get pregnant who are eligible.  

If you are pregnant, you should tell the nurse or person giving you the vaccination. 

If you are trying to get pregnant, there it no need to avoid pregnancy after COVID-19 vaccination. There is no evidence that COVID-19 vaccines effect fertility or your chances of becoming pregnant. 

The current vaccines have been shown to be effective and safe, with no negative effects on pregnancy or the baby. Having the vaccine does not increase the risk of miscarriage. 

I am eligible for COVID-19 vaccination and I’m breastfeeding. Can I still have the vaccine?

Yes, all COVID-19 vaccines used in the UK can be given to people who are breastfeeding.  

After having a vaccine, your immune system produces antibodies. These are a natural substance that helps protect you against viruses and bacteria. Antibodies your body makes can pass into breast milk and may help protect breastfed babies. There is no evidence of harm to the baby and any traces are expected to be broken down with breast milk in the baby’s stomach.

You should not stop breastfeeding to be vaccinated against COVID-19.

Page last reviewed: 17th October 2025