LONDON — For months, European countries have seesawed between craving and rebuffing AstraZeneca’s vaccine, with the shot’s fortunes rising and falling on spats over supply and on questions over the efficacy of the vaccine itself.
But few concerns have proved as disruptive to the rollout of the world’s workhorse vaccine in Europe as reports of very rare blood clots in some recipients. Many countries responded by halting the shot’s use, only to start giving it again after an all-clear from regulators at the European Medicines Agency, and then stopped inoculations a second time in certain age groups after doctors became more concerned about the clots.
On Tuesday, those concerns were reinforced yet again when a top vaccines official at the European Medicines Agency said that the vaccine was linked to extremely rare, though sometimes fatal, blood clots in a small number of recipients. It was the first indication from an international regulatory body that the clots may be a real, if very unusual, side effect of the shot.
Regulators now appear to be considering issuing their first formal warnings about the potential side effects — not only in continental Europe, which has long been wary of the shot for political and scientific reasons, but also in Britain, the birthplace of the AstraZeneca vaccine and long its biggest champion, where new data have sown concerns as well.
speedy inoculation program, have also insisted that the vaccine’s benefits far outweighed the risks. They and the company cited a lack of evidence in Britain that the clotting events were any more common than would be expected among people who had never been given AstraZeneca’s vaccine.
But the evidence changed last week when Britain reported 30 cases of the rare blood clots, 25 more than previously. This week, a prominent scientific adviser to the British government said there was “increasing evidence” of the clots being associated with the vaccine.
regulators reported 30 cases of the rare blood clots combined with low platelets among 18 million people given the AstraZeneca vaccine. That translated to roughly one case in 600,000 recipients of the vaccine.
European countries’ divergent approaches to the vaccine stem from a number of factors, including the supply of vaccines and severity of the pandemic. Marco Cavaleri, the official at the European Medicines Agency who spoke about the link between the vaccine and blood clots, said on Tuesday that those factors would likely continue to dictate how countries used the shot.
Beyond those factors, countries also took very different approaches to managing risk, scientists said. Countries that have continued using the shot were more focused on securing the overall health of their citizens. Others were more preoccupied with minimizing the risk to any single person.