Venous thrombosis: the risk of developing it “is almost 200 times higher by catching the Covid than by – Boursorama

According to a British study of 31 million people, people with the virus are also eleven times more likely to have a stroke than those vaccinated with Pfizer.

The risk of developing blood clots is much lower after being vaccinated against Covid-19 than by catching this disease, shows the largest study to date on the side effects linked to the vaccine. To achieve this result, this British study, published Friday August 27 in the British Medical Journal (BMJ), compared the medical data of 29 million people who received their first dose of Pfizer-BioNtech or Oxford-AstraZeneca between December 2020 and April 2021 with that of almost 2 million people who tested positive for the coronavirus.

While fears related to blood clots slowed down use of AstraZeneca’s vaccine, researchers found that there was indeed an “increased risk” of developing it after being vaccinated, but that risk was high. “much lower than that associated with SARS-CoV-2 infection”. The risk of developing vein thrombosis (phlebitis) is almost 200 times higher by catching the Covid (12,614 additional cases out of 10 million) than by being vaccinated with AstraZeneca (66 additional cases).

About the arterial thrombosis , no excess case was found for either vaccine, but 5,000 additional cases out of 10 million people were observed in those who had Covid. Thus, people infected with the virus are eleven times more likely to be subject to a stroke (1,699 additional cases in 10 million people) than those vaccinated with Pfizer (143 additional cases).

“The vast majority of patients will be perfectly fine with these vaccines,” told the BBC the researcher at the head of the study Julia Hippisley-Cox, affirming that it was necessary to “put in context” the “very rare cases” of blood clots. The professor of epidemiology at Oxford further pointed out that this increased risk of developing clots was concentrated over more “specific and short” periods with the vaccines (“15 to 21 days after administration of” Pfizer for stroke, ” 8 to 14 days for thrombocytopenia with AstraZeneca “) only after catching Covid-19, where the risk continues” over 28 days after infection “.

The study comes as many countries – including the UK and France – have decided to reserve the AstraZeneca vaccine for an older population, over concerns about clot formation. The English Health Service (PHE) estimates that vaccines have prevented more than 100,000 deaths in the UK, where the pandemic has claimed 132,000 lives.