Risk of blood clots 9 times higher from Covid infection than the vaccine

Infection with Covid-19 presents a “much higher” risk of developing a blood clot than a first vaccine dose, a new study has found.

The research assessed more than 29 million people who were vaccinated with the AstraZeneca and Pfizer jabs, and is the first of its kind to compare the vaccines with risks from coronavirus on such a large scale.

Risks nine times higher from Covid

The study, published in the British Medical Journal, looked at people aged 16 and over who received their first dose of either the AstraZeneca or Pfizer vaccine in England between 1 December 2020 and 24 April 2021.

Findings suggest that the risk of thrombocytopenia, a condition in which a person has a low count of platelets that help the blood to clot, is almost nine times higher in someone infected with coronavirus than in someone who has had one dose of the AstraZeneca jab.

Researchers estimated that among 10 million people vaccinated with AstraZeneca, this would result in only 107 additional cases of thrombocytopenia in the 28 days after vaccination, compared with 934 in people infected with Covid-19.

The findings come after a coroner concluded this week that award-winning BBC radio presenter Lisa Shaw died due to complications due to the AstraZeneca vaccine.

Ms Shaw passed away in May after developing a vaccine-induced thrombosis and thrombocytopenia, just over three weeks after she received her first vaccine dose.

Dr Martina Patone, a statistician at the University of Oxford, said: “We looked at hospital admission or deaths due to blood clots within 28 days of having either vaccine, and what we found is an increased risk with both vaccines, but also that the risk of blood clots is much higher if you caught Covid-19, either before or after vaccination.”

Link to increased risk of stroke

The study also found a link between the Pfizer vaccine and an increased risk of stroke, although scientists stressed that the risk is more than 10 times higher in those with Covid-19.

There were an estimated 143 extra cases of ischaemic stroke per 10 million people among those vaccinated with Pfizer, compared with 1,699 cases in those with the virus.

For every 10 million people vaccinated with AstraZeneca, there were an estimated seven additional cases of Cerebral venous sinus thrombosis, while there were 20 in people with Covid-19.