RESEARCH – According to a recent British study, while there is indeed an “increased risk” of developing thrombosis (blood clots) after being vaccinated, it remains “much lower than that associated with the infection “by the Covid-19.
Léa LUCAS with AFP –
While a wave of cases of thrombosis raised many fears last March, scientists want to be reassuring. According to their study *, the largest to date on the side effects linked to the anti-Covid vaccine, the risk of developing blood clots is much lower after being vaccinated than by catching the disease.
The researchers found that there was a “increased risk” to develop this side effect after receiving an injection of the anti-Covid vaccine, but that this risk was “much lower than that associated with SARS-CoV-2 infection”. According to them, the risk of developing venous 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).
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The vast majority of patients will be perfectly fine.
Regarding arterial thrombosis, no excess case was found for any of the vaccines approved by the European Medicines Agency (EMA), but 5,000 additional cases out of 10 million people were observed in those who had Covid. Thus, people with the virus are eleven times more likely to have 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”, study researcher Julia Hippisley-Cox told the BBC, saying that it was necessary “place in their context” the “very rare cases” blood clots.
The professor of epidemiology at Oxford pointed out that this increased risk of developing clots was concentrated over periods of longer “specific and short” with vaccines (“15 to 21 days after administration” Pfizer for stroke, “8 to 14 days for thrombocytopenia with AstraZeneca”) only after catching Covid-19, where the risk is prolonged “for 28 days after infection”.
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The study comes as many countries – including the UK – have decided to reserve the AstraZeneca vaccine for an older population, over lingering fears of clots. 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.
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* The British study, published in the British Medical Journal (BMJ) on Friday 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.
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