Thousands of British tourists visited Algarve earlier this month, but now the Portuguese government has put the U.K. on its red list for travel and requires British travelers who are not vaccinated to quarantine for two weeks after arriving in Portugal.

The Delta variant is believed to account for almost all of the U.K.’s new coronavirus cases.

For more reporting from the Associated Press, see below:

British arrivals can quarantine at their home or in a place stipulated by Portuguese health authorities. Arrivals from Brazil, India and South Africa come under the same rule.

All those entering Portugal must show either the European Union’s COVID Digital Certificate or a negative PCR test.

Health authorities in Algarve, known for its numerous beaches and sunny weather, canceled in-person classes for children up to 16 years old in a bid to break transmission chains in five towns, including the well-known vacation spots Albufeira and Faro.

The Algarve Regional Health Authority said classes would stop Monday for at least 12 days. It didn’t say how many students would be affected.

Albufeira’s 14-day cumulative coronavirus case notification rate per 100,000 people stands at 583, it said. The national rate for the Portuguese mainland is 142 and climbing.

Portugal was the worst-hit country in the world, in terms of weekly infections, in January. But an extended lockdown contained the spread.

Since the pandemic began, Portugal has officially recorded around 870,000 cases of the virus and about 17,000 deaths.