Just weeks before the start of the busy December holiday season, the U.S. Centers for Disease Control and Prevention added a handful of popular European countries to its highest advisory.For more TPG news delivered each morning to your inbox, sign up for our daily newsletter.The CDC on Monday, Dec. 6 added Portugal, Liechtenstein, France, Cyprus and Andorra to its highest designation, “CDC Level 4: COVID-19 Very High.”The CDC uses a four-level system that categorizes international destinations, with four designating a “very high” level of COVID-19. U.S. travelers are urged to avoid traveling to these destinations.The designation is likely related to the spread of the omicron coronavirus variant, deemed a “variant of concern” by the World Health Organization. According to WHO, it is less responsive to COVID-19 vaccines and may be more contagious than variants we’ve seen thus far. So far, omicron has been found on six continents and in 19 U.S. states, according to The New York Times.Late last month, the Biden Administration suspended entry to the U.S. by travelers from eight South African nations, including South Africa, Botswana and Zimbabwe. The temporary ban applies to those who have been in the affected countries within 14 days of attempted entry to the U.S. and does not include American citizens or permanent residents.Sign up for our daily newsletterEmail addressSign upI would like to subscribe to The Points Guy newsletters and special email promotions. The Points Guy will not share or sell your email. See privacy policy.The White House also imposed new testing restrictions for all travelers on U.S.-bound flights, limiting the testing window from three days to just one day.But the CDC’s designation could potentially put a damper on holiday travel, which is supposed to be a boon for the struggling international travel industry. For instance, Air France increased service between France and the U.S. this winter, anticipating demand between the two nations.But countries have also indicated they would tighten restrictions if necessary. Portugal has recorded nearly 25,000 positive coronavirus cases in the past week and 121 deaths. Due to the high cases, the country said it wouldn’t hesitate to implement new restrictions even during the winter holiday season. The government has already reimposed indoor mask wearing for all people.“We all wish that these measures were not necessary, but if they become necessary, we will take these measures,” Portugal’s Prime Minister Antonio Costa said last week.So far, however, if travelers are particularly concerned about the omicron variant, it’s not obvious with their travel booking behavior. According to a study by the travel deals website Scott’s Cheap Flights, nearly 90% of travelers said they had no intentions to cancel their holiday travel plans.