The European Medicines Agency (EMA) announced yesterday that AstraZeneca should include the risk of very rare blood clots on the list of possible side effects of its COVID-19 vaccine — and a UK vaccines advisory committee said it would be “preferable” not to give the vaccine to individuals under age 30.

After weeks of uncertainty, the announcements raise new concerns of increased hesitancy to accept the AZ shot and it remains to be seen if more than a dozen European countries that temporarily suspended or restricted inoculations in response to the reported blood clots will now resume them.

The EMA said it reviewed 62 cases of clotting in the brain and 24 instances of clotting in the abdomen, with 18 of the cases leading to the patient’s death.

“So far, most of the cases reported have occurred in women under 60 years of age within two weeks of vaccination,” the EMA said, adding that it could not identify specific risk factors.

The World Health Organization also issued a statement yesterday saying a causal relationship between the vaccine and the occurrence of blood clots with low platelets is “considered plausible but is not confirmed.”

In addition, the UK’s Medicines and Healthcare products Regulatory Agency (MHRA) said it found a slightly higher incidence of blood clots reported in the younger adult age groups, but that it is not recommending any age restrictions on vaccinations. However, the MHRA’s advisory committee on vaccines disagreed, advising that the AstraZeneca vaccine should preferably not be administered to individuals under age 30 if another vaccine is available and the patients in question don’t have an underlying health condition putting them at high risk of contracting severe COVID-19. ― Jason Scott