This time, Britain’s latest reopening is unfolding in steps — the first of which was a return to schools — followed by several weeks to measure the impact of each relaxation on the spread of the virus. In early April, Mr. Johnson plans to outline his latest thinking on travel and “Covid passports,” a form of certification for those who are inoculated or have recently tested negative.
Further reinforcing Britain’s vaccine rollout, Mr. Johnson announced that the British drug giant GlaxoSmithKline had agreed to manufacture up to 60 million doses of a vaccine developed by Novavax, a biotechnology company based in Gaithersburg, Md., at a factory in northeast England.
Scientists and public health experts generally backed the government’s latest easing, given that it is incremental and encourages mixing outdoors, where the risk of transmission is far lower than in confined spaces.
But they warned about potential vulnerabilities, like the South African variant of the virus, which is fueling the latest wave of infections in Europe and shows signs of resistance to the AstraZeneca vaccine, the one most commonly used in Britain.
“If we didn’t have the variants, I would see us as being in a very strong position,” said Devi Sridhar, head of the global public health program at the University of Edinburgh. “But we have an Achilles’ heel because if a variant develops among vulnerable people, we could be back in a very precarious situation.”
Part of the problem, she said, was Britain’s patchy approach to travel. The government has placed 35 countries on a “red list,” which requires travelers to quarantine in a hotel for 10 days. But it has stopped short of adding France, a high-risk country, because of the headache of dealing with truck drivers transporting freight across the channel.
“Either do all countries, or do no countries,” Dr. Sridhar said. “This selective approach is a little silly because you’re only delaying the problem.”