The United Kingdom, on Saturday, tightened its rules to combat COVID-19 amid the fear of Omicron, the newest variant of the virus. They tightened rules on mask-wearing and on testing of international arrivals after identifying two cases of the newest variant. This comes as other countries sought to shore up their defenses.

Amid fears that the recently identified new variant has the potential to be more resistant to the protection offered by vaccines, a longer lockdown period is looming.

Prime Minister Boris Johnson said it was necessary to take “targeted and precautionary measures” after two people tested positive for the new variant in England. The cases will be reviewed in three weeks when the scientists get to know more about them.

Johnson told a news conference that anyone arriving in England will be asked to take a mandatory PCR test for COVID-19 on the second day and must self-isolate until they provide a negative test.

And if someone tests positive for the omicron variant, then he said their close contacts will have to self-isolate for 10 days regardless of their vaccination status.

He also said mask-wearing in shops and on public transport will be required and that the vaccination program will be accelerated, without providing specific details.

“Right now this is the responsible course of action to slow down the seeding and the spread of this new variant and to maximize our defenses,” he said. “From today we’re going to boost the booster campaign.”

One of the two new cases was found in the southeastern English town of Brentwood, while the other is in the central city of Nottingham.

The British government also added four more countries — Angola, Malawi, Mozambique and Zambia — onto the country’s travel red list from Sunday. Six others — Botswana, Eswatini (formerly known as Swaziland), Lesotho, Namibia, South Africa and Zimbabwe — were added Friday.

That means anyone permitted to arrive from those destinations will have to quarantine.

(With inputs from Associated Press)