A study by the University of Oxford found that the risk of rare but sometimes fatal coagulation is about eight to 10 times higher in Covid-19 patients than in people who have received any of the first three vaccines developed. widely available in the West.
The study, which involves vaccinations from Pfizer Inc. and BioNTech SE, another from Moderna Inc. and one from AstraZeneca PLC, adds to the competing evidence of blood clotting that regulators and governments should consider as they weigh the ongoing deployment of vaccines.
US officials have recommended a break in the administration of the single-dose Covid-19 vaccine developed by Johnson & Johnson, as it is studying a possible link between the shooting and a very small number of cases of severe blood clotting. The Oxford study did not analyze patient data for recipients of the J&J shot.
The AstraZeneca shot was not approved for use in the United States, but many governments across Europe have restricted it, amid several similar cases of blood clotting involving cerebral venous thrombosis or CVD or CVST.
AstraZeneca said it is helping regulators continue to review safety and says the benefits of the vaccine outweigh its risks. J&J said it is aware of cases involving blood clots and is working with health authorities.