London appeared to be headed into a new set of stricter restrictions to curb a rapidly spreading variant of coronavirus.

U.K. Prime Minister Boris Johnson held an emergency meeting with his cabinet, and will address the public at 4 p.m. Saturday as the BBC reported that Tier-4 would be added to current a three-tier restriction system that has pubs, restaurants and cinemas closed.

The capital and southeast England will now likely fall under an even harsher set of rules, the BBC said citing unidentified sources. Plans to allow families to see each other over Christmas would also be reviewed in a blow to Johnson’s pledge to allow some households to mix over the holidays.

Chief Medical Officer Chris Whitty said that the new variant was faster spreading, and likely behind the alarming climb of case numbers in that part of the country.

Travel restrictions are also among the measures under discussion, and could be brought in as soon as Saturday, the Telegraph reported A ban on commuters traveling into London is also being considered, the newspaper reported.

Vital Measures

“There is no current evidence to suggest the new strain causes a higher mortality rate or that it affects vaccines and treatments although urgent work is underway to confirm this,” Whitty said. “Given this latest development it is now more vital than ever that the public continue to take action in their area to reduce transmission.”

As recently as Friday, Johnson refused to rule out a third U.K. lockdown to control the spread of the virus. Britain would join Italy and Austria in tightening curbs during the holiday season, with all three countries facing rapidly rising case numbers.

Viruses tend to evolve or mutate quickly, particularly those like flu that require new vaccines to be developed each year because of changes in key proteins. SARS-CoV-2 also changes, although generally at a slower pace than some other viruses because it has a self-correcting mechanism that keeps its genetic sequence relatively stable.

Other variants in the coronavirus have been reported in the past, including one in minks, which are susceptible to the virus, that was feared to be highly transmissible and was reported to the World Health Organization. Millions of farmed mink were culled, although as of Nov. 20 the WHO said the most worrying strain linked to the animals is no longer circulating in humans.