The mutant coronavirus strain that first emerged in recent months in the U.K. is 30% more deadly than original virus, British Prime Minister Boris Johnson announced January 22.

Previously, the U.K. government had said that this particular virus strain spread much more easily than the original version of SARS-CoV-2, the virus the causes COVID-19, but that it did not believe it was any more lethal. January 22's announcement reverses that assessment.

A panel of scientists that advises the British government on the threat posed by emerging respiratory viruses made the new assessment based on data from people testing positive who subsequently died in the U.K. It concluded that there was a 1.3-fold increase in the risk of death, Neil Ferguson, an epidemiologist at Imperial College London who sits on the advisory body, told Britain's ITV News.

Ferguson said that this meant that for every 1,000 people aged 60 who contracted the new strain of the virus, 13 would likely die, compared to 10 with the original strain.

The U.K. is currently facing the highest daily death tolls since the pandemic began. On January 20, 1,820 were reported dead after testing positive for COVID-19 in the U.K., a record high. Since the pandemic began, more than 94,500 people have died in the U.K. from the virus, and the country has the highest death toll per capita of any major country.

Vallance has said that the new strain, which emerged in southern England in October 2020, is between 30% and 70% more transmissible than the original virus. That increase was a major rationale for the new national lockdown in Britain. Meanwhile, many other nations, including the U.S., have imposed much more stringent travel restrictions on arrivals from the U.K., in most cases requiring negative COVID tests of all travelers.

In an evening press conference January 22, Johnson was at pains to emphasize that the new findings about the mutant strain's lethality did not change scientists' assessments that the coronavirus vaccines currently being used in the U.K. would still be highly effective against the mutant strain.

The British government has approved three coronavirus vaccines so far, including those produced by Pfizer, AstraZeneca and Moderna. To date, 5.38 million Britons, or about 8% of the country's population, have received one dose of either the Pfizer or the AstraZeneca vaccine. But it is also thought that about 1 in every 55 people in England is currently infected with coronavirus, according to Chris Whitty, the government's chief medical officer.

Since first being identified, this particular virus variant has been found in at least 60 countries, including the U.S. In the U.K., this new strain is now the dominant one in many parts of the country.

Meanwhile, the South African variant has also reached Britian. Vallance says the latest PHE data suggests at least 44 people have been detected with the South African variant. There’s no evidence the South African and Brazilian variants are able to transmit more quickly or take over and become the dominant variant, he says.

Anthony Fauci, the director of the U.S. National Institute of Allergy and Infectious Diseases, said at a White House press briefing on January 22 that the U.K. strain of the virus has so far been found in at least 20 U.S. states and that the federal government was monitoring the situation carefully. He said it was not clear yet whether the U.K. strain would become more dominant in the U.S. than the original virus.

Fauci said he was less concerned about the U.K. strain, because the existing vaccines seemed to work against it, than he was about other versions of the virus, which have emerged in South Africa and Brazil. These strains have mutations that mean the current crop of vaccines might not work as well against them, Fauci said. No cases of the South African variant have been found in the U.S. so far, he said.

Some British scientists expressed skepticism about the new analysis about the U.K. variant's lethality, however.

"Interpreting death rates when ICUs are under massive pressure is potentially misleading," Jonathan Ball[/hotlink], a professor of virology at the University of Nottingham in England tweeted.

"When ICUs are strained then standard of care can be compromised and death rates increase. Cause and effect is tricky to establish with mathematical models unless you include all the variables."