European leaders, struggling with a slow vaccination effort and fearful that highly contagious coronavirus variants could rapidly overwhelm their medical systems, moved Thursday to begin reimposing border restrictions and to speed the distribution of vaccines — even those not yet approved for use. “We are increasingly concerned about different variants of the virus,” European Commission President Ursula von der Leyen told reporters after a virtual summit of European Union leaders, saying that although the bloc intends to keep borders open for trade, it may restrict nonessential travel.

The leaders held back from endorsing a specific plan for borders. But Germany — which as the richest and most populous E.U. member often drives its discussions — proposed strict, temporary bans on travel to the E.U. from countries where mutated forms of the coronavirus are already prevalent, including Britain. The proposal would restrict E.U. citizens from returning to their home countries if they are currently in an affected country, and would therefore be more stringent than previous border measures.

German Chancellor Angela Merkel said Thursday that sharp action was necessary in the face of the more transmissible strain first identified in Britain.

“I can’t stress this strongly enough: We need to slow down the spread of this mutant virus, we mustn’t wait until this virus flares up here and is reflected in explosive new numbers,” she told reporters before the E.U. discussion. “We’d have a stronger wave of the virus, probably stronger than anything we’ve seen so far.”

The leaders also agreed to begin distributing doses of AstraZeneca’s coronavirus vaccine across Europe, so rollout can start as soon as that vaccine is approved, possibly around mid-February. Although Britain is already administering AstraZeneca inoculations, European and U.S. regulators have questioned whether there is enough data to show the vaccine is effective among older people.