LONDON — Prime Minister Boris Johnson of Britain on Wednesday announced major new restrictions to curb the spread of the coronavirus, urging people to work from home, extending a mask mandate and introducing a vaccine passport for some indoor venues, measures that his government had long resisted.
Mr. Johnson called the decision to tighten restrictions in England a “proportionate and responsible” response to the rise in Omicron cases, which he said were “growing much faster than the previous Delta variant” in Britain.
“I know this will be hard for many people but by reducing your contacts in the workplace, you will help slow transmission,” he said during an evening news conference.
The move will see the country adopt a contingency plan that was only intended to be used if new coronavirus case numbers rose to such an extent that the health system could be under threat.
Under the measures, the so-called Plan B, proof of vaccination will be needed to enter some indoor venues including nightclubs as well as large outdoor events; mask mandates in public spaces will be extended; and testing for those in contact with the Omicron variant will increase. Similar “vaccine passport” systems and mask mandates are already either in operation or planned in Northern Ireland, Scotland and Wales.
Mr. Johnson said that slowing the spread of the virus would buy Britain some time “to get more boosters into arms” and understand the answers to key questions that still remain about the Omicron variant.
Britain last week announced plans to extend its vaccine booster program to all adults in order to increase protection against the coronavirus.
The guidance to work from home will begin on Monday to give employers time to make arrangements for their workers. The government also further extended a requirement for masking in most indoor venues and will require vaccine passports for unseated indoor venues and large outdoor venues. Those measures that will come into force a week from Wednesday.
The timing of the announcement was awkward for Mr. Johnson, who has come under mounting political pressure in recent days over reports that his staff breached lockdown rules last Christmas by holding a party in Downing Street.
Earlier in the day, Allegra Stratton, a senior aide, resigned after a video emerged on Tuesday of her and other aides joking last year about whether an illicit party had been held.
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When the government outlined its contingency measures earlier this year, it said that it hoped not to have to use them. But officials added that, if they had to institute the plan, it would only ask people to work from home for a limited period.
“The government recognizes this causes more disruption and has greater immediate costs to the economy and some businesses than the other Plan B interventions. A final decision would be made based on the data at the time,” a statement said at the time.
Even before the latest announcement, Mr. Johnson had already taken one of the contingency steps — making the wearing of masks mandatory on all public transportation in England as of last week. Britain has also tightened restrictions on travelers entering the country since the Omicron variant was first reported.
Britain’s Health Security Agency, which monitors the coronavirus outbreak in the country, released new data on Wednesday that it said “suggests that Omicron is displaying a significant growth advantage over Delta” meaning that the new variant is likely to outcompete Delta and become the dominant variant in Britain.
“It is increasingly evident that Omicron is highly infectious and there is emerging laboratory and early clinical evidence to suggest that both vaccine-acquired and naturally acquired immunity against infection is reduced for this variant,” Susan Hopkins, the chief medical adviser to the agency said in a statement. “It is therefore absolutely critical that we all do everything that we can to help break the chains of transmission and slow the spread of this new variant.”