(CNN) — The US Centers for Disease Control and Prevention added three island destinations to its "high" risk category for travelers on Tuesday.
Anguilla, Jamaica and Turks and Caicos Islands were all moved to Level 3, or "high" risk for Covid-19.
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.
Level 4, previously the highest risk category, is now reserved only for special circumstances, such as extremely high case counts, emergence of a new variant of concern or health care infrastructure collapse. Under the new system, no destinations have been placed at Level 4 so far.
To recap, the three destinations moved up to the "high" risk column on Tuesday are:
• Turks and Caicos
All three destinations moved up from Level 2.
The "Level 3: Covid-19 High" category now applies to countries that have had more than 100 cases per 100,000 residents in the past 28 days.
There were about 110 destinations at Level 3 on May 31. Level 3 locations now account for just under half of the roughly 235 places monitored by the CDC.
Most of the Caribbean region is now at Level 3 with a handful of exceptions, including Cuba, Dominican Republic and Saint Kitts and Nevis, which all moved to Level 2 on Tuesday.
Many other popular travel destinations are also at Level 3.
Much of Europe has been stubbornly lodged there as the summer travel season starts. As of May 31, the following popular European destinations were among those remaining at Level 3:
• The Netherlands
• United Kingdom
It's not just European favorites that find themselves at Level 3. Numerous notable travel destinations around the world are among those in the high risk category, including the following:
• Costa Rica
• South Korea
The CDC advises that you get up-to-date with your Covid-19 vaccines before traveling to a Level 3 destination. Being "up-to-date" means you have had not only the full initial vaccinations but any boosters for which you're eligible.
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. Eight places were moved to this level on Tuesday:
• Bosnia and Herzegovina
• Dominican Republic
• Saint Kitts and Nevis
Dominican Republic, Guyana and Saint Kitts and Nevis all moved up from Level 1. The rest of the destinations moved down in risk level from Level 3.
There were about 20 destinations listed in Level 2 on May 31.
In its broader travel guidance, the CDC has recommended avoiding all international travel until you are fully vaccinated. If you're concerned about a travel-specific health situation not related to Covid-19, check here.
To be in "Level 1: Covid-19 Low," a destination must have had 49 or fewer new cases per 100,000 residents over the past 28 days. Two destinations were added to the category on May 31:
Level 1 had more than 50 entries as of Tuesday.
Finally, there are destinations the CDC has deemed to be of "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 were no additions to this category on Tuesday.
The CDC advises against travel to these places precisely because the risks are unknown. Destinations in this category include French Polynesia, the Azores, Cambodia and Tanzania.
A medical expert weighs in on risk levels
Transmission rates are just "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," she said.
"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?