(CNN) — After downgrading the risk level of many of the world's top destinations last week in conjunction with an overhaul of its travel assessments, the US Centers for Disease Control and Prevention added just one location to its "high" risk category on Monday.
The tiny Caribbean island of Saba -- a special municipality of the Netherlands known for its rugged hiking terrain and having the world's shortest commercial runway -- was moved up to Level 3.
The Level 3 "high" risk category is now the top rung in terms of risk level. Level 2 is considered "moderate" risk, and Level 1 is "low" risk. Saba had been at Level 1.
Level 4 is now reserved only for special circumstances. Under the new system, no destinations have been placed at Level 4 so far.
The overhaul comes against a backdrop of US government agencies and the public continuing to react and adapt to an ever-changing pandemic -- and sometimes in sharp disagreement.
Last week, a federal judge struck down the federal mask mandate for transportation. That sent off a quick chain of reactions, and the CDC has asked the Department of Justice to appeal. In the meantime, masks are largely optional for now on planes, trains and public transportation. (Some airports and transit systems have their own masking rules).
Saba, which moved to the CDC's "high" risk category on Monday, is known for its tiny airport runway -- the world's shortest commercial runway.
In the CDC's new system, the Level 3 "high" risk category applies to destinations that have had more than 100 cases per 100,000 residents in the past 28 days.
Saba is hardly alone on this level, however. Much of Europe is still lodged there with the summer travel season not too far away. On April 25, those popular nations included:
• United Kingdom
It's not just European favorites that find themselves at Level 3. Other popular travel spots around the world at high risk include:
• South Korea
There are almost 120 destinations at Level 3 this week, a small drop from the previous week and accounting for just over half of roughly 235 places total monitored by the CDC.
The CDC does not include the United States in its list of advisories, but on its color-coded map of the world, the CDC had it at Level 3 on Monday.
Indonesia is one of four destinations that moved to the "moderate" Covid-19 risk category on Monday.
Destinations carrying the "Level 2: Covid-19 Moderate" designation reported 50 to 100 Covid-19 cases per 100,000 residents in the past 28 days. Four destinations were moved to this level on Monday. They are:
• El Salvador
• United Arab Emirates
All four of these places had been at Level 3 last week. The CDC had only 13 destinations worldwide at the moderate risk level on Monday.
In its broader travel guidance, the CDC has recommended avoiding all international travel until you are fully vaccinated. If you're concerned about a health situation not related to Covid-19, check here.
Azerbaijan moved to "low" risk on Monday. The old town of Azerbaijan's capital of Baku is seen here.
To be in "Level 1: Covid-19 Low," a destination must have 49 or fewer new cases per 100,000 residents over the past 28 days. Three destinations were added on April 25:
The drop was most impressive for Libya, which had been at high-risk Level 3. Armenia and Azerbaijan, both in the mountainous Caucasus region where Asia and Europe meet, had been at Level 2.
This level is dominated by destinations in Africa, including Kenya, Rwanda and Senegal. Level 1 had about 55 entries total this week.
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.
There was one new entry to this category on Monday: The Gambia, a small nation in West Africa.
Attracting their fair share of visitors in this category are the Azores, Cambodia and Nicaragua. 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've moved into "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," 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.
There are other factors to weigh in addition to transmission rates, according to Wen.
"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?