A highly infectious variant of Covid-19 that has spread around the world since it was first discovered in Britain late last year is between 30 percent and 100 percent more deadly than previous dominant variants, researchers said in London on Wednesday.

In a study that compared death rates among people in Britain infected with the new SARS-CoV-2 variant - known as B.1.1.7 - against those infected with other variants of the Covid-19-causing virus, scientists said the new variant's mortality rate was "significantly higher"...