LONDON — With a rapid and successful vaccine campaign on track, the path seemed clear not long ago for Prime Minister Boris Johnson to scrap all of England’s coronavirus rules on June 21, ending curbs that he resisted imposing in the first place.
But on Monday, Mr. Johnson postponed by four weeks the moment dubbed “freedom day” by the tabloids after a spike in cases of a highly transmissible new variant that may cause more serious disease than earlier variants. Restaurants and pubs in England, while open, will still have to observe social distancing rules indoors, limiting capacity, and nightclubs and theaters will remain firmly closed.
The decision, which will be reviewed in two weeks, sent a warning to the world that even well-vaccinated nations remain at risk and angered a noisy caucus of libertarian lawmakers within Mr. Johnson’s own party.
At present, overall new cases in Britain are averaging around 8,000 per day and are doubling every week in the worst affected areas. Hospital admissions have begun rising. And the impact of the Delta variant across the country has already incited alarm in other European countries including Germany, which has introduced a travel ban.
In Britain, around four-fifths of adults have received one dose and more than half have had a second shot. But people with only a single dose remain susceptible to cases of the Delta variant — more so than to earlier versions of the virus, scientists said. And an unabated surge of infections in younger, unvaccinated people could ignite a dangerous wave of hospitalizations.
That has helped convince many epidemiologists that lifting restrictions now could, in a worst-case scenario, produce as many hospital cases as in the first wave of the pandemic, overwhelming the National Health Service just as it is trying to cope with a backlog of procedures that were postponed during the pandemic.
At a news conference at Downing Street, Mr. Johnson said it was sensible to wait “just a little longer” before lifting the curbs, noting that “even if the link between infection and hospitalization has been weakened, it has not been severed.”
Expressing confidence that he would be able to remove the remaining restrictions on July 19, Mr. Johnson added that “at a certain stage, we are going to have to learn to live with the virus and to manage it as best we can.”
Since first being sampled in Britain almost four months ago, the Delta variant, which was initially detected in India, has swept across the country, outcompeting even the dangerous Alpha variant that took hold earlier. Recent studies show that 96 percent of new cases now are from the Delta variant.
And the variant now appears to be outpacing other versions of the virus in parts of the United States and Canada, too, with some scientists saying that they expected that trend to continue.