Skip to main content

Coronavirus (COVID-19) vaccines safety and side effects

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.

How COVID-19 vaccines are developed and tested

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
  • people with different health conditions

How COVID-19 vaccines are approved and monitored

The vaccines approved for use in the UK have met strict standards of safety, quality and effectiveness set out by the independent Medicines and Healthcare products Regulatory Agency (MHRA).

Any COVID-19 vaccine that is approved must go through all the clinical trials and safety checks all other licensed medicines go through. The MHRA follows international standards of safety.

Once the MHRA has approved a vaccine for use, it is closely monitored to continue to make sure it is safe and effective.

Side effects of the COVID-19 vaccine

Like all medicines, the COVID-19 vaccine can cause side effects, but not everyone gets them. Any side effects are usually mild and go away within a few days.

Common side effects

Most side effects of the COVID-19 vaccine are mild and should not last longer than a week, such as:

  • a sore arm from the injection
  • feeling tired
  • a headache
  • feeling achy
  • feeling or being sick

You may also get a high temperature or feel hot or shivery 1 or 2 days after your vaccination. You can take painkillers such as paracetamol if you need to. If your symptoms get worse or you're worried, call 111.

If you have a high temperature that lasts longer than 2 days, a new, continuous cough or a loss or change to your sense of smell or taste, you may have COVID-19. Stay at home and get a test.

You cannot catch COVID-19 from the vaccine, but you may have caught it just before or after your vaccination.

Very rare side effects

Serious side effects from the COVID-19 vaccine are very rare.

Allergic reactions

Tell healthcare staff before you are vaccinated if you've ever had a serious allergic reaction.

You should not have the COVID-19 vaccine if you have ever had a serious allergic reaction (including anaphylaxis) to:

  • a previous dose of the same vaccine
  • any of the ingredients in the vaccine

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

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.

Find out more about COVID-19 vaccination and blood clotting on GOV.UK

Urgent advice: Call 111 immediately if:

You get any of these symptoms starting from around 4 days to 4 weeks after being vaccinated:

  • a severe headache that is not relieved with painkillers or is getting worse
  • a headache that feels worse when you lie down or bend over
  • a headache that's unusual for you along with blurred vision, feeling or being sick, problems speaking, weakness, drowsiness or seizures (fits)
  • a rash that looks like small bruises or bleeding under the skin
  • shortness of breath, chest pain, leg swelling or persistent abdominal (tummy) pain

Page last reviewed: 10 June 2021
Next review due: 24 June 2021