Boris Johnson reports Britain’s first known death from the omicron coronavirus variant

"I think the idea that this is somehow a milder version of the virus, that's something we need to set on one side and just recognize the sheer pace at which it accelerates through the population," Johnson told reporters during a visit to a vaccination clinic in London. He urged people to quickly increase their protection with a booster shot.

Long lines formed outside vaccination clinics on Monday, with people waiting to get a first, second or third dose.

The prime minister's office did not immediately offer any details about the person who died - age, vaccination status or any underlying conditions.

It's possible that this death is the first in the world to be officially tied to the new variant, though that in itself is of limited significance. There may have been others that weren't genetically sequenced to determine the variant involved.

The U.K. Health Security Agency said Monday there were 10 patients in hospitals across England, aged 18 to 85, diagnosed with omicron on or before admission, with the majority having received two doses of coronavirus vaccine.

Hospital admissions lag infections, and officials here worry that a coming crush of patients could overwhelm the National Health Service. The new strain is now spreading faster in Britain than it has in South Africa, where the first cases were detected. And, unlike South Africa, Britain was already dealing with a surge of delta variant cases.

Early reports from South Africa suggest that omicron may be milder on average than the delta variant it is competing with. But even a small portion of severe cases among a huge number of infections could put strain British hospitals.

Health Secretary Sajid Javid said Monday that hospitalizations and deaths are forecast to "dramatically increase" in the coming weeks.

Speaking to lawmakers in the House of Commons on Monday afternoon, he said omicron would become the dominant variant in London in the next 48 hours. It already represented 20 percent of all new cases in England, with cases doubling every two to three days.

"No variant of covid-19 has spread this fast," Javid said in Parliament.

Earlier, he called the growth rate "phenomenal."

On Saturday, Britain reported 633 new confirmed cases of omicron; on Sunday, 1,239; and on Monday, another 1,576, for a total of 4,713 confirmed cases of the variant in the country.

Scientists suspect there are in reality 10,000s of new but unreported infections a day.

"The best thing we can do is all get our boosters," Johnson said.

He announced in a televised address on Sunday that Britain would try to get booster shots to everyone age 18 and over by New Year's Day, bringing forward an earlier deadline by a month.

"A tidal wave of omicron is coming," Johnson warned. "And I'm afraid it is now clear that two dose of vaccine are simply not enough to give the level of protection we all need."

To reach that target, the NHS will need to carry out about a million vaccinations a day, double what it had been doing. The government plans to deploy 42 medical teams from the military to assist. General practitioners in the National Health Service are also being told to cancel other nonessential appointments if necessary to meet the booster deadline.

There's still much that the world doesn't know about omicron, including just how effective vaccines - and boosters - might be against it. British scientists say answers are likely to come fast, over the next few weeks, as infections spread and real-world studies continue.

On Friday, the U.K. Health Security Agency reported that two doses of either AstraZeneca or Pfizer vaccines offered poor protection against symptomatic infection by omicron.

The primary two doses of the Pfizer vaccine gave 30 to 40 percent protection against symptomatic illness from 25 weeks after second dose. AstraZeneca provided even less protection, though the sample size of the study was so small that scientists are cautious.

The good news: The health services agency said preliminary studies found that a third, booster jab of Pfizer would likely raise protection from omicron considerably - to between 70 and 75 percent.

On Monday, scientists reported research that showed a steep drop-off in the neutralizing antibody response to the omicron variant. The laboratory studies were carried out with blood samples from people vaccinated with the two doses of either AstraZeneca or Pfizer. The studies did not examine the response after a third booster shot. That research is coming soon.

Teresa Lambe, a co-author of the study and professor at the Jenner Institute at the University of Oxford, said neutralizing antibodies might not tell the whole story and that other immune responses against omicron may be stimulated by the vaccines.

Lambe said early studies by others also suggested that a booster dose of existing vaccines may be effective against omicron.

She urged people to get a third shot.

At one vaccination clinic in Streatham, in southwest London, more than 100 people were still waiting in line as night fell - the winter sun sets here around 4 p.m. on Monday.

Sabrina Singh, 44, a child-care worker, said she wasn't influenced by Johnson's plea - "in my opinion, he talks rubbish" - but was encouraged to get a booster shot by her eldest daughter, who is recovering from covid after being sick for two weeks.

"She is concerned about me because I'm a heavy smoker," Singh said. "I think all of this," she added, waving at a line of people mostly under 45, "is so we can have normal Christmas this year. Or as normal as possible. I think that's why everyone is rushing."

Rob Flanagan, 33, a graphic designer, who had finally made it to the front of the queue after two hours, said he had come because "this was first day I was eligible, I think that's everyone here really. Everyone is looking quite young."

Flanagan said he started to alter his behavior in recent weeks, as the number of variant cases started to climb sharply. "I'm working from home, reducing socializing, concerned about public transport, definitely feeling worried about being out and about, and will wear a mask on the street as opposed to just on a bus or supermarket," he said.

Others who tried to book appointments via the NHS website were told to try again later. The government confirmed that the site crashed at one point on Monday.

Johnson is facing another rough week. In addition to the coronavirus surge, he has been immersed in a scandal about several alleged Christmas parties at Downing Street during a strick lockdown last year.

Rebels from his own Conservative Party have threatened to vote against new stricter public health measures. They are opposed to anything that smacks of a fourth "lockdown," as well as mandatory vaccination and use of "vaccine passports."

Starting this week, people are being encouraged to work from home, wear face masks in most indoor venues and show proof of vaccination or a negative test for entrance into places with large crowds. The government also said daily testing would replace quarantines for those who come into contact with someone who has tested positive.

Normally, rapid coronavirus tests can be ordered at no charge on a government website. But on Monday, the government website read: "Sorry, there are no more home test kits available right now."