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Last updated: 8 Apr 2021 1:47 pm

COVID-19 vaccination and blood clotting

The UK vaccination programme has been very successful with more than 30 million people vaccinated and more than 6,000 lives already saved.

Recently there have been reports of a very rare condition involving blood clots and unusual bleeding after vaccination. This is being carefully reviewed but the risk factors for this condition are not yet clear.

Although this condition remains extremely rare there appears to be a higher risk in people who have had the first dose of the AstraZeneca (AZ) vaccine. Around 4 people develop this condition for every million doses of AZ vaccine doses given.

This is seen slightly more often in younger people and tends to occur between 4 days and 2 weeks following vaccination.

This condition can also occur naturally, and clotting problems are a common complication of COVID-19 infection. An increased risk has not yet been seen after other COVID-19 vaccines but is being carefully monitored.

Age Risk from COVID-19 Benefit of vaccination Risk of vaccination
Over 50 years of age or having underlying medical conditions Low - catching infection, passing on infection 1 dose – more than 80% reduction: deaths, hospitalisation, intensive care Uncommon - sore arm, feeling tired, headache, general aches, flu like symptoms
  Moderate - Long COVID 2 doses – more than 95% reduction: deaths Extremely rare - clotting problems
  Very high - hospitalisation, intensive care admission, death    
30 to 49 years of age Low - hospitalisation, intensive care admission, death 1 dose – between 60% and 70% reduction: catching infection, passing on infection Common - sore arm, feeling tired, headache, general aches, flu like symptoms
  Moderate - Long COVID 2 doses – more than 85% reduction: catching and passing on infection Extremely rare - clotting problems
  High - catching mild infection, passing on infection    
18 to 29 years of age Very low - hospitalisation, intensive care admission, death 1 dose – between 60% and 70% reduction: catching infection, passing on infection Very common - sore arm, feeling tired, headache, general aches, flu like symptoms
  Moderate - Long COVID 2 doses – more than 85% reduction: catching and passing on infection Extremely rare - clotting problems
  Very high - catching mild infection, passing on infection    

Although serious side effects are very rare, if you experience any of the following from around 4 days to 4 weeks after vaccination you should seek medical advice urgently:

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

What you should do next

All older adults (including health and social care workers over 50 years of age), care home residents, health and social care workers (includes unpaid carers and family members of those who are immunosuppressed) and adults with certain medical conditions were prioritised in the first phase of the programme because they were at high risk of the complications of COVID-19.

The Medicines and Healthcare products Regulatory Agency (MHRA) and the Joint Committee on Vaccination and Immunisation (JCVI) advises that you should still receive any of the available COVID-19 vaccines. The benefits of vaccination in protecting you against the serious consequences of COVID-19 outweigh any risk of this rare condition. You should also complete your course with the same vaccine you had for the first dose.

If your first dose was with AZ vaccine without suffering any serious side effects you should have the second dose on time as you may still be at high risk of the complications of COVID-19. Having the second dose will give you higher and longer lasting protection.

The MHRA and the JCVI advises that all adults in this age group (including health and social care workers) should still receive any of the available COVID-19 vaccines.

The benefits of vaccination in protecting you against the serious consequences of COVID-19 outweigh any risk of this rare condition. You should also complete your course with the same vaccine you had for the first dose.

The MHRA and the JCVI advises that all adults in this age group (including health and social care workers) should still receive any of the available COVID-19 vaccines. The benefits of vaccination in protecting you against the serious consequences of COVID-19 outweigh any risk of this rare condition. You should also complete your course with the same vaccine you had for the first dose.

Currently JCVI has advised that it is preferable for people under 30 to have a vaccine other than AZ. If you choose to have another COVID-19 vaccine you may have to wait to be protected. You may wish to go ahead with the AZ vaccination after you have considered all the risks and benefits for you.

If you have already had a first dose of AZ vaccine without suffering any serious side effects you should complete the course. This includes people aged 18 to 29 years who are health and social care workers, unpaid carers and family members of those who are immunosuppressed. It is expected that the first dose of the vaccine will have given you some protection, particularly against severe disease.

Further information can be found at NHS.UK.

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