By Marnie Hunter, CNN
(CNN) -- For the second week in a row, the US Centers for Disease Control and Prevention did not add a single new destination to its highest-risk Level 4 category for travel.
More than a dozen destinations, including Canada and several Caribbean nations, moved down from Level 4 to Level 3 on Monday.
The CDC places a destination at Level 4 "very high" risk when more than 500 cases per 100,000 residents are registered in the past 28 days. The Level 3 "high" risk category applies to destinations that have had between 100 and 500 cases per 100,000 residents in the past 28 days.
In total, 14 destinations moved to Level 3 on April 4:
• Antigua and Barbuda
• Saint Lucia
All 14 places were previously listed at Level 4. CDC advises avoiding travel to Level 4 countries.
CDC thresholds for travel health notices are based primarily on the number of Covid-19 cases in a destination.
While the CDC does not include the United States in its list of advisories, it is part of its color-coded global map of travel risk levels. On Monday, the United States joined its neighbor to the north in moving down to Level 3 color coding on the map.
Declining risk levels are a bright spot on the travel landscape. Still, almost 100 destinations remained at Level 4 on April 4 -- about 40% of the nearly 240 places the CDC covers.
You can view the CDC's risk levels for any global destination on its travel recommendations page.
In its broader travel guidance, the CDC has recommended avoiding all international travel until you are fully vaccinated.
Changes at Level 2, Level 1 and 'unknown' status
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. The five new entries to Level 2 on April 4 are:
• South Africa
• Dominican Republic
All but Iraq had been at Level 3. Iraq was previously at Level 4.
To be in "Level 1: Covid-19 Low," a destination must have fewer than 50 new cases per 100,000 residents over the past 28 days. Six places moved to Level 1 on Monday:
All six had been at Level 2. Level 1 is dominated by destinations in Africa. Only seven places in Level 1 are outside of Africa.
Finally, there are destinations for which the CDC has an "unknown" risk because of a lack of information. Usually, but not always, these are small, remote places or places with ongoing warfare or unrest.
The CDC made three additions to the unknown category on Monday: French Guiana, Greenland and Ukraine.
The ongoing war in Ukraine has undoubtedly disrupted testing, treatment and the collection of Covid-19 case numbers.
The Azores, Cambodia, Macau and Tanzania are among the more-visited locations currently listed in the unknown category. The CDC advises against travel to these places precisely because the risks are unknown.
A medical expert weighs in on risk levels
Transmission rates are "one guidepost" for travelers' personal risk calculations, according to CNN Medical Analyst Dr. Leana Wen.
We're in "a phase in the pandemic where people need to make their own decisions based on their medical circumstances as well as their risk tolerance when it comes to contracting Covid-19," Wen said.
"You should interpret Level 4 to mean this is a place with a lot of community transmission of Covid-19. So if you go, there is a higher chance that you could contract the coronavirus," said Wen, who is an emergency physician and professor of health policy and management at the George Washington University Milken Institute School of Public Health.
Some people will decide the risk is too high for them, Wen said. "Other people will say, 'Because I am vaccinated and boosted, I am willing to take on that risk.'
"So this really needs to be a personal decision that people weigh understanding that right now the CDC is classifying the different levels based on community transmission rates, and basically only that," Wen said. "They're not taking into account individual circumstances."
More considerations for travel
There are other factors to weigh in addition to transmission rates, according to Wen.
"The transmission rates are one guidepost," Wen said. "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.
"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. That's very different. Those are very different levels of risk."
Vaccination is the most significant safety factor for travel since unvaccinated travelers are more likely to become ill and transmit Covid-19 to others, Wen said.
And it's also important to consider what you would do if you end up testing positive away from home. Where will you stay and how easy will it be to get a test to return home?
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