LONDON — Prime Minister Boris Johnson of Britain said on Sunday evening that its coronavirus vaccine booster program would be accelerated to counter what he called a “tidal wave” of cases from the rapidly spreading Omicron variant.
Mr. Johnson said the British government would now aim to offer all eligible adults a booster shot by the end of this year, a month earlier than the goal he set on Nov. 30 to deliver these millions of shots by the end of January.
“No one should be in any doubt: There is a tidal wave of Omicron coming,” Mr. Johnson said in a videotaped address, “and I’m afraid it is now clear that two doses of vaccine are simply not enough to give the level of protection we all need.”
Mr. Johnson, who has been under extreme pressure for days after the disclosure that his aides held a holiday party in breach of coronavirus restrictions last year, did not announce any major new social-distancing restrictions. But the government raised the Covid alert level from three to four — its second-highest level — amid signs that Omicron was spreading rapidly throughout the country.
In raising the alert level, the chief medical officers of England, Scotland, Wales and Northern Ireland, declared in a statement that the “early evidence shows that Omicron is spreading much faster than Delta and that vaccine protection against symptomatic disease from Omicron is reduced.”
Under what Mr. Johnson called the “Omicron Emergency Boost,” the government will offer booster shots to adults ages 18 and older by New Year’s Day. Adults are eligible for a booster shot three months after their second shot. Britain has distributed 23.1 million booster shots, reaching 40.2 percent of people aged 12 and above.
To reach the new goal, Mr. Johnson said the National Health Service would have to defer some other medical procedures between now and the end of the year. He said the government would deploy 42 military planning units to help open additional vaccination centers and mobile units.
“If we don’t do this now, the wave of Omicron could be so big that cancellations and disruptions, like the loss of cancer appointments, would be even greater next year,” Mr. Johnson said. “To hit the pace we need, we’ll need to match the N.H.S.’s best vaccination day yet — and then beat it day after day.”
“This will require an extraordinary effort,” he added.
The videotaped address seemed calculated in part to seize the offensive in advance of a politically perilous week in which Mr. Johnson will face a difficult vote in Parliament on Covid restrictions he announced last week, as well as by an election in which the Conservative Party is at risk of losing a once-safe seat.
Mr. Johnson faces a potential mutiny by members of his Conservative Party, who have threatened to vote against the new restrictions, which include urging people to work from home, wear face masks in more indoor settings, and to show a vaccine certification to enter nightclubs, and events with large audiences.
The prime minister’s credibility has also come under question after reports that members of his staff held Christmas parties in 10 Downing Street, at a time when the public was instructed not to meet with friends or family members.