A study from the University of Oxford found that the risk of rare but sometimes fatal blood clotting is about eight to 10 times greater in patients with Covid-19 than in people who received one of the first three Western-developed vaccines that are widely available to be.
The study, with vaccinations from Pfizer Inc. and BioNTech SE, another from Moderna Inc. and one from AstraZeneca PLC, adds to the competing evidence regarding blood clotting that regulators and governments may need to consider when weighing the continued use of vaccines.
US officials have recommended a pause in the administration of the single-dose Covid-19 vaccine developed by Johnson & Johnson, as they are studying a possible link between the injection and a very small number of cases of severe blood clotting. The Oxford study did not look at patient data for recipients of the J&J admission.
The AstraZeneca injection is not approved for use in the US, but many governments across Europe have limited it, amid several cases of similar blood clotting with cerebral vein thrombosis, or CVT or CVST.
AstraZeneca has said it is helping regulators continue with safety assessments and says the benefits of the vaccine outweigh the risks. J&J said it is aware of the cases of blood clots and is working with health authorities.