The EU's medicines regulator says unusual blood clots should be listed as a very rare side effect of the AstraZeneca vaccine for Covid-19.
After a study looking at 86 European cases, the European Medicines Agency (EMA) concluded the benefits of the vaccine outweighed the risk.
The report reflected data on 25 million Europeans administered with the jab.
The EMA could not list specific risk factors such as age or gender, but most blood clot cases were women under 60.
Separately, the UK's vaccine advisory body said that under-30s there were to be offered an alternative jab to AstraZeneca due to the blood clots issue. Some 79 people had suffered rare blood clots after vaccination by the end of March in the UK - 19 of whom had died.
And the World Health Organization's advisory vaccine safety panel said on Wednesday that although a blood clot link was "plausible" it was "not confirmed" and the cases were "very rare" among 200 million people vaccinated with AstraZeneca globally.
More than 132 million Covid-19 infections have been recorded across the world, along with more than 2.8 million deaths, according to Johns Hopkins University research.
What did the EMA find?
There were two main elements to its report - the link with blood clots and how this could affect vaccination programmes.
The EMA had concluded there was a "possibility of very rare cases of blood clots combined with low levels of blood platelets occurring within two weeks of vaccination" with the AstraZeneca jab.
Most of the 86 cases studied in the European Economic Area (the EU, Iceland, Norway and Liechtenstein) up to 22 March were in women under 60. Eighteen were fatal.
But EMA executive director Emer Cooke said there was no available evidence of "specific risk factors such as age, gender, or previous medical history of clotting disorders".
On the safety side, she said: "Our safety committee... has confirmed that the benefits of the AstraZeneca vaccine in preventing Covid-19 overall outweigh the risks of side effects."
Ms Cooke added: "This vaccine has proven to be highly effective - it prevents severe disease and hospitalisation, and it is saving lives."
AstraZeneca has said its studies have found no causal link with blood clots.
Ms Cooke said that one "plausible explanation for these rare side effects is an immune response to the vaccine".
The condition is similar to one seen in people who have been treated with the drug heparin, a blood thinner used to prevent the formation of clots.
In some cases there has been a potentially dangerous immune-driven adverse reaction to the drug, leading to a condition called heparin-induced thrombocytopenia, or HIT.
What action could EU nations take now?
Although the EMA evaluates and supervises medicine use for all of the EU, including drug approval, this does not mean there has been unity on tackling Covid-19.
After a virtual meeting of EU health ministers on Wednesday to discuss the EMA findings, European Commissioner for Health Stella Kyriakides said in a statement: "Our decisions should now be based on the scientific work of EMA, and a rigorous, continuous assessment of risks and benefits.
"I have today called on Health Ministers to follow a coordinated approach across Europe to improve public confidence."
But earlier Belgium announced it would restrict AstraZeneca to those aged 56 and above and then Italy said it was recommending reserving it for the over 60s. But Italy also said there was no evidence to stop people having a second dose of AstraZeneca.
Spain later said that it was restricting AstraZeneca to those between 60 and 64.
Countries within the bloc have diverged widely on vaccination campaigns and on the use of the AstraZeneca jab.
France recommends that AstraZeneca vaccinations be given only to those aged 55 or over. In Germany it is over 60, plus high-priority groups. Norway, not an EU member, and Denmark have a full suspension.
Germany also says its under-60s who have received an AstraZeneca first dose should now get a different vaccine for their second.
France, Finland and Norway could consider similar moves.
Studies are still being done on the effectiveness of mixed vaccines.
The EU has ordered 400 million doses of the Oxford-AstraZeneca vaccine but has been locked in a dispute over supply, saying AstraZeneca has not met its obligations.
Nevertheless, some EU nations have not used the AstraZeneca vaccines that have been supplied, with a drop in public confidence being blamed.
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