As Britain found itself even more isolated on Tuesday because of a new variant of the coronavirus, the European Commission advised European Union members to lift blanket bans on travellers, recommending testing or quarantines instead. And one vaccine expert said that there was no evidence at the moment to suggest that the current vaccine would have to be adapted.

Dr. Ugur Sahin, the co-founder of BioNTech, which, with Pfizer, developed the first vaccine approved in the West to combat the coronavirus, cautioned that it would be two weeks before full results from laboratory studies would allow for a fuller understanding of how the mutations might impact the effectiveness of the vaccine.

“We believe that there is no reason to be concerned until we get the data,” he said.

If an adapted vaccine were necessary, it could be ready within six weeks, Dr. Sahin told a news conference on Tuesday. But it would require additional approval from regulators, which could increase the wait-time, he said.

But governments around the world were not waiting for a more complete picture of the new variant, instead racing to seal their borders to travellers from Britain. More than 50 governments put in place some sort of regulation related to the situation in Britain. And officials in London warned that the lockdown measures in effect in the capital and southern England might need to be expanded.