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 earlier said there was a "realistic possibility" that the variant was not only more contagious but also more lethal.
Now, they say it is "likely" that it is linked to an elevated risk of hospitalisation and death.
The British government did not publicly announce the updated findings on the new Covid-19 variant, known as B117. But it posted a document on the findings on an official website last Friday.
The reasons for a higher death rate are not entirely clear.
Some evidence suggests that people infected with the variant may have greater 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.
Scientific advisers to the British government said on Saturday that the new findings laid bare the dangers of countries easing restrictions as the variant takes hold.
It has spread to at least 82 countries, and is being transmitted 35 per cent to 45 per cent more easily than other variants in the United States, scientists estimate.
US officials have suggested that the variant could become the dominant source of infection there by next month.
"The overall picture is one of something like a 40 per cent to 60 per cent increase in hospitalisation risk and risk of death," Dr Neil Ferguson, a public health researcher and scientific adviser to the British government, said.
Most Covid-19 cases, even those caused by the new variant, are not fatal.
And the scientists were relying on studies that examined a small proportion of overall deaths.
The scientists also struggled to account for the presence of underlying illnesses in people infected with the new variant, and whether the cases originated in nursing homes.
They were largely limited to studying people who had tested positive for the virus at community testing sites, rather than in hospitals. A quirk of hospital tests means that many cannot detect an altered gene that is often used as a proxy for the variant.
One of the studies that fed the new findings offered alarming, though very preliminary, signs that the elevated risk from the new variant held especially among black and Asian Britons.
That raised the notion that because the variant was more contagious, it could be hitting vulnerable populations harder.
Overall, the government scientists' assessment that the variant was "likely" to be linked to a higher risk of death still signalled only 55 per cent to 75 per cent 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 Dr 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 per cent to 50 per cent more transmissible, although some scientists put the figure higher than that.
Since the first sample of the variant was collected in England in September, it has become the dominant source of infection in Britain, accounting for over 90 per cent of cases in many parts of the country.
An easing of the nation's stringent lockdown could trigger another sharp rise in cases caused by the variant. Roughly 117,000 people have died from the coronavirus in Britain, half since November as the variant spread.
"This has been quite catastrophic in terms of mortality," said Dr Ferguson. "And that's a result of both the increased transmissibility and the increased lethality."
A study by the London School of Hygiene & Tropical Medicine, one of those the government scientists relied on, offered rough estimates of the variant's effect.
It examined 3,382 fatalities, 1,722 of them in people infected with the variant, and estimated that the risk of death was 58 per cent higher among cases caused by the variant.
For men aged 55 to 69, for example, that raised the overall risk of death to 0.9 per cent from 0.6 per cent. For women in that age group, the overall risk rose to 0.3 per cent from 0.2 per cent.
"Calculating when we can lift restrictions has to be influenced by this," Associate Professor in cellular microbiology Simon Clarke at the University of Reading said of the new report.
He added that the findings vindicated Britain's move to raise an alarm about the variant in December and then publish evidence that it was potentially more lethal.
"They didn't hold the data back," Prof Clarke said.
"They were very upfront about how uncertain things were."
Singapore reported its first B117 case on Dec 23, a 17-year-old Singaporean student who had returned from Britain on Dec 6.
Since then, both community and imported cases have tested positive for the B117 strain.