LONDON — British authorities recommended Wednesday that the AstraZeneca COVID-19 vaccine not be given to adults under 30 where possible because of strengthening evidence that the shot may be linked to rare blood clots.

The recommendation came as regulators in the United Kingdom and the European Union emphasized that the benefits of receiving the vaccine continue to outweigh the risks for most people — even though the European Medicines Agency said it had found a “possible link” between the shot and the rare clots. British authorities recommended that people under 30 be offered alternatives to AstraZeneca. But the EMA advised no such age restrictions, leaving it up to its member-countries to decide whether to limit its use.

Several countries have already imposed limits on who can receive the vaccine, and any restrictions are closely watched since the vaccine, which is cheaper and easier to store than many others, is critical to global immunization campaigns and is a pillar of the U.N.-backed program known as COVAX that aims to get vaccines to some of the world’s poorest countries.

“This is a course correction, there’s no question about that,” said Jonathan Van-Tam, England’s deputy chief medical officer.

Van-Tam said the effect on Britain’s vaccination timetable — one of the speediest in the world — should be “zero or negligible,” assuming the National Health Service receives expected deliveries of other vaccines, including those produced by Pfizer and Moderna.

EU and U.K. regulators held simultaneous press conferences Wednesday to announce the results of investigations into reports of blood clots that sparked concern about the rollout of the AstraZeneca vaccine.

The EU agency described the clots as “very rare” side effects. Dr Sabine Straus, chair of EMA’s Safety Committee, said the best data is coming from Germany, where there is one report of the rare clots for every 100,000 doses given, although she noted far fewer reports in the U.K. Still, that’s less than the clot risk that healthy women face from birth control pills, noted another expert, Dr. Peter Arlett.

The agency said most of the cases reported have occurred in women under 60 within two weeks of vaccination — but based on the currently available evidence, it was not able to identify specific risk factors. Experts reviewed several dozen cases that came mainly from Europe and the U.K., where around 25 million people have received the AstraZeneca vaccine.

“The reported cases of unusual blood clotting following vaccination with the AstraZeneca vaccine should be listed as possible side effects of the vaccine,” said Emer Cooke, the agency’s executive director. “The risk of mortality from COVID is much greater than the risk of mortality from these side effects.”

Arlett said there is no information suggesting an increased risk from the other major COVID-19 vaccines.

The EMA’s investigation focused on unusual types of blood clots that are occurring along with low blood platelets. One rare clot type appears in multiple blood vessels and the other in veins that drain blood from the brain.

“We are not advising a stop to any vaccination for any individual in any age group,” said Wei Shen Lim, who chairs Britain’s Joint Committee on Vaccination and Immunization. “We are advising a preference for one vaccine over another vaccine for a particular age group, really out of the utmost caution.”

In March, over a dozen countries, mostly in Europe, suspended their use of AstraZeneca over the blood clot issue. Most restarted — some with age restrictions — after the EMA said countries should continue using the potentially life-saving vaccine. Britain, which relies heavily on AstraZeneca, continued to use it.