LONDON — British government scientists are increasingly finding the coronavirus variant first detected in Britain to be linked to a higher risk of death than other versions of the virus, a devastating trend that highlights the serious risks and considerable uncertainties of this new phase of the pandemic.
The scientists said last month that there was a “realistic possibility” that the variant was not only more contagious than others but also more lethal. Now, they say in a new document that it is “likely” that the variant is linked to an increased risk of hospitalization and death.
The British government did not publicly announce the updated findings, which are based on roughly twice as many studies as its earlier assessment and include more deaths from Covid-19 cases caused by the new variant, known as B.1.1.7. It posted the document on a government website on Friday.
The reasons for an elevated death rate are not entirely clear. Some evidence suggests that people infected with the variant may have higher viral loads, a feature that could not only make the virus more contagious but also potentially undermine the effectiveness of certain treatments.
But scientists are also trying to understand how much of the increased risk of death may stem from the propensity of the variant to spread very easily through settings like nursing homes, where people are already vulnerable.
No matter the explanation, scientific advisers to the British government said on Saturday, the new findings laid bare the dangers of countries easing restrictions as the variant takes hold.
The variant has spread to at least 82 countries and is being transmitted 35 to 45 percent more easily than other variants in the United States, scientists recently estimated. American officials have suggested that the variant could be the dominant source of infection there by March.
“The overall picture is one of something like a 40 to 60 percent increase in hospitalization risk, and risk of death,” Neil Ferguson, an epidemiologist and scientific adviser to the British government, said in an interview on Saturday. Referring to the tight restrictions on socializing that are in effect across Britain, he said, “It reinforces the policy measures in place.”
Most Covid-19 cases, even those caused by the new variant, are not fatal. And the government scientists were relying on studies that examined a small proportion of overall deaths.
Over all, the government scientists’ assessment that the variant was “likely” to be linked to a higher risk of death still only signaled 55 to 75 percent confidence in the finding.
“I think these results are possibly genuine, although there are still several limitations and we need to understand what causes it,” said Muge Cevik, an infectious disease expert at the University of St. Andrews in Scotland and a scientific adviser to the British government.
She added that “there are other explanations of this increased severity,” among them that the variant may “transmit disproportionately in settings with frailer people,” like nursing homes because it is more transmissible.
The biggest danger of the new variant remains its propensity to spread: It is thought to be 30 to 50 percent more transmissible, though some scientists put the figure higher than that.