AstraZeneca Vaccine Carries Slightly Higher Risk of Bleeding Disorders, Study Shows But the research, involving 2.53 million adults in Scotland, found that the vaccine’s benefits outweighed the small risks. A dose of the AstraZeneca vaccine being prepared in Newcastle, Scotland, in January.Credit...Owen Humphreys/PAMPC, via Associated Press June 9, 2021, 3:23 p.m. ET People receiving the Covid vaccine made by Oxford-AstraZeneca had a slightly increased risk of a bleeding disorder, and possibly other rare blood problems, researchers reported on Wednesday. The findings, from a study of 2.53 million adults in Scotland who received their first doses of either the AstraZeneca vaccine or the one made by Pfizer-BioNTech, were published in the journal Nature Medicine. About 1.7 million of the shots were the AstraZeneca vaccine.