Through guidelines and warnings from the Centers for Disease Control and Prevention and the State Department, the United States has advised against travel to some European countries, including Austria, Germany, Denmark, Belgium, Greece, Norway, Ireland and the Czech Republic.

Austria has taken the hardest line so far, becoming the first Western country to reimpose a full nationwide lockdown, allowing people to leave their homes only to go to work or buy essential items like groceries and medicine.

The shutdown will last at least 10 days and could be extended until Dec. 13, the Austrian government said. During this period, leisure travel to Austria is banned and tourist attractions, including Christmas markets, museums and theaters, are closed. Tourists already in the country who are unable to rearrange their flights home will be permitted to stay in hotels but must comply with lockdown rules.

On Saturday, Britain announced that it would require all visitors to take a PCR test by the end of their second day after arrival and self-isolate until they receive a negative test. Also on Saturday, the Swiss government announced a 10-day quarantine requirement for arrivals from Britain after cases of the new variant were identified there.

Germany has identified two cases of the new variant and is grappling to contain a fourth wave of the virus. The government has indicated that lockdowns could be a possibility, even for those who are vaccinated. Christmas markets have been canceled in Saxony and Bavaria, bars and clubs are closed, and restaurants are operating with reduced hours.

The Czech Republic and Slovakia, which have recorded some of the highest infection rates in Europe, have banned unvaccinated people from restaurants, hotels, bars and hairdressers, even if they have a negative coronavirus test.

The Netherlands returned to a partial lockdown on Nov. 13 for at least three weeks, with restaurants and shops closing early and spectators banned from sporting events. The Dutch government is exploring ways to restrict unvaccinated people from indoor venues, a measure that has spurred riots and protests across the country. On Saturday, the Swiss government announced a 10-day quarantine requirement for arrivals from Britain after cases of the new variant were identified there.