England tightens restrictions as more Omicron cases found.

Thirteen cases of the Omicron variant have been identified in England, the British government confirmed on Tuesday. Britain has announced an extension of its vaccination program, mask mandates and travel restrictions in an attempt to stem the spread of the variant.

Sajid Javid, Britain’s health secretary, confirmed the increase in cases during a news conference and said officials did not yet know whether all of the cases were linked to travel to southern Africa, raising concerns about potential community transmission.

“Is there likely to be community transmission? I think we have to be realistic there is likely to be, as we are seeing in other European countries,” Mr. Javid said. “We would expect cases to rise as we now actively look for cases.”

Hours earlier, Scotland’s first minister, Nicola Sturgeon, confirmed that nine cases of the new variant had been identified in Scotland, all linked to a single private event. That brings the total number of known cases in Britain to 22.

Prime Minister Boris Johnson, speaking during the same news conference as Mr. Javid, said it was vital that Britons do their part by getting booster shots.

“I know the frustration that we all feel with this Omicron variant, the sense of exhaustion that we could be going through this all again,” Mr. Johnson said. But “that is the wrong thing to feel,” he added, because the country is in a much better position than this time last year thanks to high vaccination rates.

At almost every step of the pandemic, Britain has been an outlier. It locked down later than its European neighbors in March 2020, rolled out vaccines faster than almost any other country, and threw off virtually all restrictions over the summer in an audacious bid to return life to normal.

But with worries about Omicron flaring across the world, Britain has fallen in line with its neighbors. The government quickly banned travel from 10 African countries, made face masks compulsory in shops and on public transportation, and on Monday announced a huge acceleration of its vaccine program — including expanding eligibility for booster shots to anyone 18 or older.

Britain’s approach is still looser than that of countries like Austria, which imposed a lockdown on unvaccinated people, and Greece, which announced on Tuesday that it would make vaccination mandatory for people 60 or older. In Britain, people can still gather in pubs without masks, for example, and officials keep promising weary Britons a normal Christmas.

But Mr. Javid said the government was prepared to shelve its laissez-faire approach, at least for the moment, to stave off another wave of infections.

“Our experience of fighting this virus has shown us that it’s best to act decisively and swiftly when we see a potential threat,” Mr. Javid said in Parliament on Monday. “If it emerges that this variant is no more dangerous than the Delta variant, then we won’t keep measures in place for a day longer than necessary.”