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17th March, 20215 min read

Should I be worried about the Oxford/AstraZeneca vaccine and blood clots?

Medical reviewer: Healthily's medical team
Author: Ceri Moorhouse
Last reviewed: 08/04/2021
Medically reviewed

All of Healthily's articles undergo medical safety checks to verify that the information is medically safe. View more details in our safety page, or read our editorial policy.

Some countries have paused using the Oxford/AstraZeneca coronavirus vaccine after a number of people who were given it had blood clots afterwards.

While many of these countries have since started using it again, advice on how it should be used has now changed.

Read on to learn more about the link between blood clots and the Oxford/AstraZeneca vaccine, and what the experts say.

When to get medical help urgently

If you have any of the following symptoms more than 4 days and within 28 days of COVID-19 vaccination, you should get medical help urgently:

  • new onset of severe headache, which is getting worse and does not respond to simple painkillers
  • an unusual headache which seems worse when lying down or bending over, or may be accompanied by blurred vision, nausea and vomiting, difficulty with speech, weakness, drowsiness or seizures
  • new unexplained pinprick bruising or bleeding
  • shortness of breath, chest pain, leg swelling or persistent abdominal pain

The European Medicines Agency (EMA) has said that unusual blood clots combined with low blood platelets should be listed as a very rare side effect of the Oxford/AstraZeneca vaccine.

It said in a statement: “EMA is reminding healthcare professionals and people receiving the vaccine to remain aware of the possibility of very rare cases of blood clots combined with low levels of blood platelets occurring within 2 weeks of vaccination. So far, most of the cases reported have occurred in women under 60 years of age within 2 weeks of vaccination. Based on the currently available evidence, specific risk factors have not been confirmed.”

The EMA has said a possible reason for this could be because of how the immune system responds to the vaccine. It has asked for more research to be done to get more information.

It adds that the overall benefit of the vaccine still outweighs the risk: “COVID-19 is associated with a risk of hospitalisation and death. The reported combination of blood clots and low blood platelets is very rare, and the overall benefits of the vaccine in preventing COVID-19 outweigh the risks of side effects.”

The chance of developing these blood clots after having the vaccine appears to be extremely low – 1 in 250,000. By comparison, the chance of dying in a road accident within a year is 1 in 20,000 in the UK and 1 in 7,000 in the US.

Who shouldn’t get the Oxford/AstraZeneca vaccine?

People who had blood clots after their first dose of the Oxford/AstraZeneca vaccine shouldn’t get their second dose of this vaccine.

Other groups of people should only get the Oxford/AstraZeneca vaccine if their doctor advises them that the benefits outweigh the risks. These groups include:

  • people at higher risk of blood clots because of a medical condition
  • pregnant women

Some countries are not giving the vaccine to people in certain age groups. For example, some European countries and Canada are not giving it to people under 55. And in the UK, people under 30 will be offered an alternative vaccine.

What should I do if I’m worried about the safety of the vaccine?

“If you're due to have the vaccine, the safest thing to do is to go ahead and have it, unless you are in a group that has been advised to have an alternative vaccine, ” says Healthily Chief Medical Officer, Professor Maureen Baker. “For most people, the risk of severe illness or death from COVID-19 far exceeds any risk from the vaccine. We should also remember that every drug or vaccine, even very commonly used ones such as aspirin or paracetamol, can potentially have serious, or even fatal, side-effects.”

“Generally, it isn't possible to choose which vaccine you can have. You should take the first one offered to you. The approved vaccines are safe and effective and have now been administered to hundreds of millions of people across the world.”

Key points

  • advice on how the Oxford/AstraZeneca COVID-19 vaccine should be used has changed
  • if you have any of the symptoms above, you should get medical help urgently
  • the European Medicines Agency (EMA) has said that unusual blood clots combined with low blood platelets should be listed as a very rare side effect of the vaccine
  • EMA has said the overall benefit of the vaccine still outweighs the risk
  • people who had blood clots after their first dose of the Oxford/AstraZeneca vaccine shouldn’t get their second dose
  • other groups of people should only get the Oxford/AstraZeneca vaccine if their doctor advises them that the benefits outweigh the risks

COVID-19: Blood clots and the Oxford-AstraZeneca coronavirus vaccine - what does the data say? [Internet]. Sky News. 2021 [cited 16 March 2021]. Available here

AstraZeneca U. Update on the safety of COVID-19 Vaccine AstraZeneca [Internet]. Astrazeneca.com. 2021 [cited 16 March 2021]. Available here

Covid-19: Evidence does not suggest AstraZeneca jab linked to clots, MHRA says [Internet]. BBC News. 2021 [cited 16 March 2021]. Available here

COVID-19 Vaccine AstraZeneca: PRAC investigating cases of thromboembolic events - vaccine’s benefits currently still outweigh risks Update European Medicines Agency [Internet]. European Medicines Agency. 2021 [cited 16 March 2021]. Available here

MHRA response to the precautionary suspensions of COVID-19 Vaccine AstraZeneca [Internet]. GOV.UK. 2021 [cited 16 March 2021]. Available here

Which countries have stopped using AstraZeneca’s COVID vaccine? [Internet]. Aljazeera.com. 2021 [cited 16 March 2021]. Available here

Blood clots [Internet]. nhs.uk. 2021 [cited 16 March 2021]. Available here

Blood Clots: Signs, Symptoms, Risks and More - Healthily [Internet]. Healthily. 2021 [cited 16 March 2021]. Available here

Covid-19: EU states to resume AstraZeneca vaccine rollout [Internet]. BBC News. 2021 [cited 19 March 2021]. Available here

COVID-19 Vaccine AstraZeneca: benefits still outweigh the risks despite possible link to rare blood clots with low platelets - European Medicines Agency [Internet]. European Medicines Agency. 2021 [cited 19 March 2021]. Available here

WHO statement on AstraZeneca COVID-19 vaccine safety signals [Internet]. Who.int. 2021 [cited 19 March 2021]. Available here

UK regulator confirms that people should continue to receive the COVID-19 vaccine AstraZeneca [Internet]. GOV.UK. 2021 [cited 19 March 2021]. Available here

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Important: Our website provides useful information but is not a substitute for medical advice. You should always seek the advice of your doctor when making decisions about your health.

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