Study: 'Extremely small' risk of blood clots with AstraZeneca COVID vaccineTwo independent UK studies published yesterday in PLOS Medicine find only a very slight risk of blood clots in the brain after receipt of the AstraZeneca/Oxford COVID-19 vaccine and none after the Pfizer/BioNTech vaccine.
Both studies were led by University of Edinburgh researchers.The first study involved analysis of the electronic health records of 46 million adults in England, 21 million of whom were vaccinated during the study period of December 2020 to March 2021.After adjusting for demographic characteristics and underlying illnesses, the risk of blood clots blocking an artery or vein was slightly lower in the 28 days after vaccination with either the AstraZeneca or AstraZeneca vaccine in people 70 years and older.
In people younger than 70, the risk was similar in the 28 days but rose slightly for venous blood clots in the brain after AstraZeneca.This finding corresponded to an estimated excess risk of 0.9 to 3 per million, depending on age and sex, about twice that of unvaccinated people.
The authors, however, said the benefits of COVID-19 vaccination likely exceed the risk."We were able to show that these risks occur only in people under 70 years old with the Oxford-AstraZeneca vaccine and that the increase in risk is extremely small—no more than a few people per million vaccinated," lead author William Whiteley, BM BCh, PhD, said in a PLOS news release.The second study involved a dataset of 11.6 million adults in England, Scotland, and Wales from December 2020 through June 2021.