UK regulator says some evidence AstraZeneca clots occur more in women than men

Britain’s medicine regulator on Thursday said there was some evidence that uncommon blood clots linked to AstraZeneca’s COVID-19 vaccine occurred more in women than in men, adding that the difference in incidence was small.

British officials have previously only said that the incidence of the clots was linked to age, and that a link with sex had not been established, noting that more women had been vaccinated then men.

“There is now some evidence that the reported incidence rate is higher in females compared to men although this is not seen across all age groups and the difference remains small,” said the Medicines and Healthcare products Regulatory Agency (MHRA) in its weekly updates on the clots.

There has been scrutiny of the AstraZeneca vaccine on the issue of the very rare clots, with a higher incidence in younger people. Some countries, including Britain, have recommended that only people over a certain age get the shot.

In the latest weekly figures, the MHRA said that the case incidence of the rare clots and low platelet levels was 10.5 per million doses, compared to 9.3 per million last week.

There were 242 cases of the clots, with 6 occurring after second doses. Up to April 28 there had been 22.6 million first doses of the AstraZeneca vaccine given in Britain, with 5.9 million second doses.

“The advice remains that the benefits of the vaccine outweigh the risks in the majority of people,” the MHRA said.