A study from Oxford University found that the risk of rare but sometimes fatal blood clotting was about eight to ten times greater in Covid-19 sufferers than in people who received one of the first three Western-developed vaccines.
The study, which included vaccinations from Pfizer Inc. and BioNTech SE, one of Moderna Inc. and one of AstraZeneca PLCs, among others, contributes to competing evidence of blood clotting that regulators and governments may need to consider as they weigh the continued deployment of vaccines.
U.S. officials have recommended a break in the administration of the single-dose Covid-19 vaccine developed by Johnson & Johnson as they study a possible link between the shot 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 survey.
The AstraZeneca shot has not been approved for use in the US, but many European governments have restricted it, amid several cases of similar blood clotting that include cerebral venous thrombosis, or CVT, or CVST.
AstraZeneca said it helps regulators continue their safety reviews and says the benefits of the vaccine outweigh the risks. J&J said that they are aware of the cases where blood clots are involved and that they work with health authorities.