LONDON — With a rapid rollout of spectacularly successful vaccines, 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 shuttered.
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 new cases are averaging around 8,000 per day and are doubling every week. Hospital admissions have begun rising. And the impact of the Delta variant across England has already sparked 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 the 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.
Since first being sampled in Britain almost four months ago, the Delta variant, which was first detected in India, has swept across the country, outcompeting even the dangerous variant called Alpha that took hold earlier. Recent studies show that 96 percent of new infections now are with the Delta variant.
Scientists remain at odds over exactly how serious a threat it poses, however, with some arguing that the most dire predictions about rising hospitalizations underestimate the effect even the current level of vaccinations have on breaking the link between the number of new infections and hospitalizations and deaths.
The optimists could point to reassuring news Monday from Public Health England: Full courses of the Pfizer and AstraZeneca vaccines offer extremely strong protection against hospitalization in cases of the Delta variant.