UK Prime Minister Boris Johnson
Early evidence suggests the variant of coronavirus that emerged in the UK may be more deadly.
Prime Minister Boris Johnson made the disclosure at a news conference on Friday, noting that, in addition to spreading more quickly, there is evidence that the new variant "may be associated with a higher degree of mortality."
However, there is still huge uncertainty around the numbers - and vaccines are still expected to work against the variant.
The data come from mathematicians comparing death rates in people infected with either the new or the old versions of the virus.
The new more infectious variant, which was first detected in September, has already spread widely across the UK.
Studies have already shown it can spread more easily than other versions of the virus.
It has spread to more than 50 other countries.