The four destinations moved to Level 4, the highest risk category, are:
• Czech Republic
With their ornate architecture and rich cultures, the Czech Republic and Hungary have been two of the darlings of Central European travel ever since the fall of the Iron Curtain in the late 20th century.
Iceland -- the "land of fire and ice" -- is a big draw among outdoor adventurists. And little charming Guernsey is a self-governing British Crown dependency in the English Channel not far from the coast of France.
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.
Previously, all four destinations had been listed in the Level 3 category of "Covid-19 High" risk. By moving to Level 4, they join the ranks of other travel favorites in Europe and elsewhere. They include:
• US Virgin Islands
In all, more than 70 destinations are currently at Level 4. The United Kingdom and British Virgin Islands have been lodged at Level 4 since July 19.
New entries on Level 3
Salar de Uyuni, the world's largest salt flat, is one of Bolivia's otherworldly landscapes.
Ronaldo Schemidt/AFP via Getty Images
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 three updates this week.
• Papua New Guinea
The move was actually good news for the Bahamas, a tourism-dependent destination, and Papua New Guinea -- both had been at Level 4.
For Bolivia, known for its otherworldly landscapes, the move signals an increase in cases as it previously was listed at Level 2.
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.
Update on Level 2
The CDC moved exotic Morocco, in the northwest corner of Africa, down from Level 3 to Level 2.
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.
Six destinations moved into Level 1 on November 15:
Finally, there are destinations for which the CDC has an "unknown" risk because of a lack of information. As of November 15, that list included Madagascar, Cambodia, Nicaragua and Macau.
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.