LONDON (Reuters) — British Prime Minister Boris Johnson was discussing with his senior ministers on Saturday what urgent action to take after it was confirmed that a new strain of the COVID-19 virus could spread more quickly and lead to a surge in cases.

England’s Chief Medical Officer Chris Whitty said that while there was no current evidence the variant of the novel coronavirus caused a higher mortality rate or impacted vaccines, urgent work was underway to confirm this.

“We have alerted the World Health Organisation and are continuing to analyse the available data to improve our understanding,” Whitty said in a statement.

The government said on Monday that a rise in infections across London and southeast England might be linked to a new, more transmissible variant of the virus.

Johnson will hold a news conference with Whitty and the government’s chief scientific adviser at about 1600 GMT amid suggestions that he will announce new urgent measures to try to address the rise in cases caused by the variant COVID-19 strain.

Britain reported 28,507 new COVID-19 cases on Friday and 489 deaths, with the reproduction “R” number estimated to be between 1.1 and 1.2, meaning the number of cases is rapidly increasing.

Johnson said on Friday he hoped England would not need to go into a third lockdown after Christmas and has so far resisted calls to change plans to ease restrictions for five days over the festive period, allowing three separate households to meet indoors.

Much of the country, including London, is currently in the highest of a three-tier system of restrictions to curb the spread. The Daily Telegraph newspaper said ministers could now announce curbs on travel between southeast England, including the capital, and the rest of the country.

“Failing to act decisively now, will mean further suffering. We must keep asking ourselves ‘are we doing enough, are we acting quickly enough’,” Jeremy Farrar, director of the Wellcome Trust and a member of the government’s Scientific Advisory Group for Emergencies (SAGE), said on Twitter.

The opposition Labour Party said the tiered system had failed to curb the virus’s spread.

“It has been apparent for some days that the virus is again out of control in parts of the country,” said Jonathan Ashworth, Labour’s health spokesman.

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Additional reporting by Elizabeth Piper; Editing by Ros Russell, William Maclean, Catherine Evans