(CNN) — The US Centers for Disease Control and Prevention added two northwestern European countries to its list of "very high" risk travel destinations this week amid a surge in cases in Europe that a WHO official has said is "of grave concern."
The Netherlands and Luxembourg were added to the CDC's highest risk category Monday afternoon. There were both previously listed as Level 3, or "high" risk for Covid-19.
Hans Kluge, a World Health Organization regional director, said Thursday that every country in Europe and Central Asia is "facing a real threat of Covid-19 resurgence or already fighting it."
"The current pace of transmission across the 53 countries of the European Region is of grave concern," Kluge said.
The Faroe Islands in the North Atlantic Ocean, a self-governing archipelago that is part of the kingdom of Denmark, were also added to the Level 4 category. In the Caribbean, the Cayman Islands received a Level 4 designation.
Destinations that fall into the CDC's "Covid-19 Very High" Level 4 category have had more than 500 cases per 100,000 residents in the past 28 days.
People should avoid traveling to locations designated with a "Level 4" notice, the CDC recommends. Anyone who must travel should be fully vaccinated first, the agency advises.
These four destinations moved to Level 4 on November 8:
• Cayman Islands
• Faroe Islands
All four locations were previously listed as Level 3 or "high" risk.
Many popular international vacation spots remained lodged at the highest level of alert, evidence of Covid-19's continuing grip.
There were 80 countries at Level 4 as of November 8. The current list of Level 4 destinations includes: Austria, Barbados, Belgium, Botswana, Greece, Maldives, Switzerland, Turkey and the United Kingdom.
New entries on Level 3
The Level 3 category -- which applies to destinations that have had between 100 and 500 cases per 100,000 residents in the past 28 days -- had four updates this week:
• Sint Maarten
• Republic of Congo
Being placed in Level 3 was a sign of progress in all four locations, which were previously listed in the Level 4 category.
There are other factors for travelers to consider beyond the Covid-19 incidence rates that figure prominently in the CDC's travel notices, according to CNN Medical Analyst Dr. Leana Wen.
"The transmission rates are one guidepost. Another is what precautions are required and followed in the place that you're going and then the third is what are you planning to do once you're there," said Wen, an emergency physician and professor of health policy and management at the George Washington University Milken Institute School of Public Health.
"Are you planning to visit a lot of attractions and go to indoor bars? That's very different from you're going somewhere where you're planning to lie on the beach all day and not interact with anyone else," said Wen, who is also author of a new book, "Lifelines: A Doctor's Journey in the Fight for Public Health."
Most importantly, travelers should be vaccinated, she said.
Updates in Level 2
There were two updates to the Level 2 category this week. Nepal and United Arab Emirates both moved down from Level 3.
Destinations carrying the "Level 2: Covid-19 Moderate" designation have seen 50 to 99 Covid-19 cases per 100,000 residents in the past 28 days.
Keep in mind the CDC list updates weekly, and the situation in any country can change for better or worse from week to week.
Level 1 and no ratings
In the category of "Level 1: Covid-19 Low" destinations, fewer than 50 new cases per 100,000 residents have been logged over the past 28 days.
Five destinations moved into Level 1 on November 8:
• Côte d'Ivoire (Ivory Coast)
Finally, there are destinations for which the CDC has an "unknown" risk because of a lack of information. As of November 8, that list included Madagascar, Cambodia, Nicaragua and Syria.
In its broader travel guidance, the CDC has recommended avoiding all international travel until you are fully vaccinated.
"Fully vaccinated travelers are less likely to get and spread Covid-19. However, international travel poses additional risks, and even fully vaccinated travelers might be at increased risk for getting and possibly spreading some Covid-19 variants," the agency said.