The COVID-19 variant first identified in the U.K. is more deadly than the original strain, according to a new study that confirms findings reported by Prime Minister Boris Johnson in January.

For every death among patients infected with earlier versions of the coronavirus, there have been 1.64 fatalities in people who caught the new variant, according to research that tracked more than 100,000 cases. That’s a higher ratio than earlier analyses that showed the new strain might be about one-third more lethal, as well as being more contagious.

Mutant versions of the virus are fueling an increase in infections across parts of Europe. In the U.K., where the new strain is dominant, cases and deaths have plummeted since early January to levels not seen since autumn as vaccinations race ahead and Johnson moves cautiously on easing a national lockdown.

Studies have shown that U.K.-approved vaccines from AstraZeneca Plc, Moderna Inc., and a partnership of Pfizer Inc. and BioNTech SE are effective against the U.K. variant, though protection from another strain identified in South Africa is more variable.

The new study, published in the British Medical Journal, said individuals infected with the U.K. strain were 32% to 104% more likely to die than those who caught previously circulating variants, with the central estimate being 64%. The absolute risk of death remains low, researchers said, with 227 deaths among about 55,000 people infected with the mutant virus, compared with 141 among the same number of cases with earlier strains.