Coronavirus (COVID-19) vaccines side effects and safety-NHS UK

United Kingdom National Health Service

Millions of people have had a coronavirus (COVID-19) vaccine and the safety of the vaccines continues to be monitored. Reports of serious side effects are very rare.

There is an increased risk of myocarditis (inflammation of the heart muscle) and pericarditis (inflammation of the lining outside the heart) after vaccination with COVID-19 mRNA Vaccine BNT162b2 . These conditions can develop within just a few days after vaccination and have primarily occurred within 14 days. They have been observed more often after the second vaccination, and more often in younger males. Following vaccination, you should be alert to signs of myocarditis and pericarditis, such as breathlessness, palpitations and chest pain, and seek immediate medical attention should these occur.

As with any vaccine, COVID-19 mRNA Vaccine BNT162b2 may not fully protect all those who receive it. No data are currently available in individuals with a weakened immune system or who are taking chronic treatment that suppresses or prevents immune responses.

If you are immunocompromised and receive an additional dose of mRNA Vaccine BNT162b2, it may still not provide full immunity to COVID-19 and you should continue to maintain physical precautions to help prevent COVID-19. [Information for UK recipients on Pfizer/BioNTech COVID-19 vaccine (Regulation 174) Updated 24 December 2021]

Common side effects

Like all vaccines, COVID-19 mRNA Vaccine BNT162b2 can cause side effects, although not everybody gets them.

Most side effects are mild or moderate and go away within a few days of appearing. If side effects such as pain and/or fever are troublesome, they can be treated by medicines for pain and fever such as paracetamol.

Side effects may occur with following frequencies:

Very common: may affect more than 1 in 10 people

  • injection site: pain, swelling
  • tiredness
  • headache
  • muscle pain
  • chills
  • joint pain
  • diarrhoea
  • fever

Common: may affect up to 1 in 10 people

  • redness at injection site
  • nausea
  • vomiting

Uncommon: may affect up to 1 in 100 people

  • enlarged lymph nodes
  • feeling unwell
  • arm pain
  • insomnia
  • injection site itching
  • allergic reactions such as rash or itching
  • feeling weak or lack of energy/sleepy
  • decreased appetite
  • excessive sweating
  • night sweats

Rare side effects: may affect up to 1 in 1,000 people

  • temporary one sided facial drooping
  • allergic reactions such as hives or swelling of the face

Very rare side effects: may affect up to 1 in 10,000 people

  • inflammation of the heart muscle (myocarditis) or inflammation of the lining outside the heart (pericarditis) which can result in breathlessness, palpitations or chest pain

Not known (cannot be estimated from the available data)

  • severe allergic reaction
  • extensive swelling of the vaccinated limb
  • swelling of the face (swelling of the face may occur in patients who have had facial dermatological fillers)
  • a skin reaction that causes red spots or patches on the skin, that may look like a target or “bulls-eye” with a dark red centre surrounded by paler red rings (erythema multiforme)

Some people have reported a sudden feeling of cold with shivering/shaking accompanied by a rise in temperature, possibly with sweating, headache (including migraine-like headaches), nausea, muscle aches and feeling unwell, starting within a day of having the vaccine and usually lasting for a day or two.

If your fever is high and lasts longer than three days, or you have other persistent symptoms, this might not be due to side effects of the vaccine and you should seek appropriate medical advice according to your symptoms.[Information for UK recipients on Pfizer/BioNTech COVID-19 vaccine (Regulation 174) Updated 24 December 2021]

Very rare side effects

Allergic reactions

Most people with allergies (including food or penicillin allergies) can be vaccinated against COVID-19.

Tell healthcare staff before you’re vaccinated if you’ve ever had a serious allergic reaction (including anaphylaxis). They may ask what you’re allergic to, to make sure you can have the vaccine.

Serious allergic reactions to the COVID-19 vaccines are very rare.

If you do have a reaction, it usually happens in minutes. Staff giving the vaccine are trained to deal with allergic reactions and treat them immediately.

If you have a serious allergic reaction to the 1st dose of a vaccine, you should not have the same vaccine for your 2nd dose.

Blood clotting

The MHRA is carrying out a detailed review of reports of an extremely rare blood clotting problem affecting a small number of people who had the Oxford/AstraZeneca vaccine.

It’s not yet clear why it affects some people.

The COVID-19 vaccine can help stop you getting seriously ill or dying from COVID-19. For people aged 40 or over and those with other health conditions, the benefits of being vaccinated with the Oxford/AstraZeneca vaccine outweigh any risk of clotting problems.

For people under 40 without other health conditions, it’s preferable for you to have the Pfizer/BioNTech or Moderna vaccine instead of the Oxford/AstraZeneca vaccine.

Heart inflammation (myocarditis)

There have been rare cases of inflammation of the heart (myocarditis) reported after COVID-19 vaccination. Most people who had this recovered following rest and simple treatments.

Get urgent medical advice if you have any of these symptoms within a few days of being vaccinated:

  • chest pain
  • shortness of breath
  • a fast-beating, fluttering or pounding heart (palpitations)

COVID-19 vaccines have to go through several stages of clinical trials before they can be approved for use. Clinical trials are where a vaccine or medicine is tested on volunteers to make sure it works and is safe. The approved COVID-19 vaccines have been tested on thousands of people in the UK and around the world, including:

people from different ethnic backgrounds
people aged between 18 and 84
children and young people aged between 12 and 17
people with different health conditions
All vaccines used in the UK must be approved by the independent Medicines and Healthcare products Regulatory Agency (MHRA).

The MHRA makes sure the vaccines meet strict international standards for safety, quality and effectiveness. Once a vaccine is approved, it’s closely monitored to continue to make sure it is safe and effective.


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