As the Journal article explains, early reports suggested that relatively young women who received the vaccines were most likely to experience clots, but the EMA reported last week that it could not identify any particularly high-risk groups from its data on the AstraZeneca vaccine.
The apparent bias towards women could be the result of many countries prioritising vaccination for health-care workers, who are predominantly female.
Nonetheless, identifying the possible risk risk factors could allow regulators to better determine the risk of the vaccine relative to the risks of COVID-19, which vary with age and other factors, notes the Nature article.
How to respond to blood clot concerns
Call 111 immediately if you get any of these symptoms associated with blood clotting following vaccination.