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Platelets and COVID-19 vaccines

Platelets in vaccine associated thrombosis in Covid-19

The UK can be proud of the success of the speed of development of the Oxford-AZ vaccine in response to the pandemic. The vaccine has saved tens of thousands of lives world-wide and is helping the UK to come out of lockdown. 

In March, the first reports of life-threatening blood clots (thrombosis) were reported in a very small number of individuals who had been administered the Oxford-AZ vaccine in the previous two weeks.  UK researchers were among the first to identify the thrombosis and to show that it is caused by platelets that have been activated by antibodies present in a small number of individuals.  These studies were performed by researchers in London and Birmingham and include members of the Platelet Charity.  The reporting also led to way to treat and potentially prevent the thrombosis using drugs that block platelet activation. 

The results were rapidly published in the leading journals so that the evidence was provided to scientists around the world, and was critical for the government’s decision to offer alternative vaccines to people aged under 40.  

Research is continuing to understand the mechanisms that give rise to activation of platelets in a very small number of individuals so that the vaccination programme can be continued to be rolled out around the world. 

Current medical advice

In the UK, the latest advice can be found by visiting the NHS website coronavirus pages  and on vaccination at the vaccine page. Specific information and advice on the coronavirus vaccine and these rare episodes of blood clotting (thrombosis) can be found at

Current advice

The Society Supports the advice from Government and healthcare professionals. Vaccination provides protection from the potentially serious effects of Covid-19 and provides benefit to yourself and others. 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:

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