Blood Clot Risk from COVID-19 Higher than After Vaccines: Study

The chance of developing cerebral venous sinus thrombosis was nearly 10 times higher in the two weeks following a diagnosis of SARS-CoV-2 infection than after receiving an mRNA vaccine, a data analysis finds.

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A COVID-19 diagnosis is associated with a 39-in-1-million chance of developing a rare blood clot condition, compared with about a 4-in-1-million chance after receiving the Pfizer or Moderna mRNA vaccines against the disease, according to a data analysis led by researchers at the University of Oxford. The study, posted Wednesday (April 14), has not yet been peer reviewed. The findings add weight to concerns that suspending the use of other vaccines, namely, AstraZeneca’s and Johnson & Johnson’s adenovirus vector–based shots, might not be worth the tradeoff of leaving people without protection against SARS-CoV-2.

Last month, some European countries halted use of the AstraZeneca jab due to blood clot concerns. The European Medicines Agency later determined cerebral venous sinus thrombosis (CVST, also known as cerebral venous thrombosis or CVT) is an extremely rare side effect of the shot. Then, this week, US health authorities recommended a ...

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Meet the Author

  • Shawna Williams

    Shawna was an editor at The Scientist from 2017 through 2022. She holds a bachelor's degree in biochemistry from Colorado College and a graduate certificate and science communication from the University of California, Santa Cruz.
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