The US Centers for Disease Control and Prevention unveiled its new system for travel risk assessments on Monday.

Many European nations are now considered at "high" risk for Covid-19, along with other marquee destinations around the world.

The new system places destinations into the following categories:

• Level 3: High risk for Covid-19

• Level 2: Moderate risk for Covid-19

• Level 1: Low risk for Covid-19

• Unknown: Not enough data to assess risk

The big change comes at Level 4, which was regularly used for places considered "very high" risk for travelers. Level 4 will no longer be routinely used for that purpose.

Instead, a Level 4 notice is reserved, in the new system, for only special circumstances.

Those circumstances include "extremely high case counts, emergence of a new variant of concern or healthcare infrastructure collapse," the CDC said. "Other factors that may be considered include information such as vaccination rate and hospitalization rate."

The CDC did not assign any destinations to Level 4 -- "Special Circumstances/Do Not Travel" -- on its Travel Recommendations website page on Monday.

Levels 3, 2 and 1 will still be primarily determined by the previous formula of 28-day incidence or case counts.

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.

On Monday, a federal judge in Florida struck down the Biden administration's mask mandate for airplanes and other public transport methods, and a Biden administration official says the order is no longer in effect while the ruling is reviewed.

CDC's Level 3

In the 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.

Among the countries in Level 3 is France, which was the most visited country in the world in 2019 before the pandemic, according to the UN's World Tourism Organization.

But other stalwarts of the European travel scene are in the "high" risk category, too. On April 18, they included:

• Germany

• Greece

• Ireland

• Italy

• Portugal

• Spain

• United Kingdom

It's not just European favorites that find themselves on this rebooted list. Other popular travel spots around the world also at Level 3 include:

• Brazil

• Canada

• Egypt

• Malaysia

• Mexico

• South Korea

• Thailand

In all, there were just over 120 destinations at Level 3 late Monday afternoon. The CDC reports on roughly 235 places total.

The CDC advises that you be up-to-date with your Covid-19 vaccines before traveling to a Level 3 destination. "Up-to-date" includes not only the full initial vaccinations but any boosters for which you're eligible.

The CDC does not include the United States in its list of advisories.

Level 2

Destinations carrying the "Level 2: Covid-19 Moderate" designation report 50 to 100 Covid-19 cases per 100,000 residents in the past 28 days.

It had only 11 entries on Monday, scattered in spots around the globe. The most notable names were:

• Bolivia

• Peru

• South Africa

• Sri Lanka

• Turks and Caicos Islands

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.

If you're concerned about a health situation not related to Covid-19, check here.

Level 1

This level is dominated by destinations in Africa and had almost 55 entries in the first week under the new system.

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.

Some of the noteworthy places include:

• Colombia

• Dominican Republic

• India

• Jamaica

• Kenya

• Philippines

• Senegal

Unknown

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 Azores, Cambodia and Nicaragua are among the 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'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.

Some people will decide the risk is too high for them in the higher categories, 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? (CNN)

•File: Mi Teleferico is an aerial cable car in the city of La Paz, Bolivia. This South American country is at Level 2

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