Christmas trees in Plaza Unidad de Italia (Piazza Unità d'Italia) in Trieste, Italy, on December 12, 2021. (Photo by Manuel Romano/NurPhoto via Getty Images)
CNN  — 

The US Centers for Disease Control and Prevention added three nations to its highest-risk category for travel on Monday, including tourist favorite Italy.

In its weekly update of Covid-19 travel advisories, the CDC also added giant, frigid Greenland and the tiny, tropical East African island nation of Mauritius to its “Level 4: Covid-19 Very High” category.

Typically, the CDC places a destination at Level 4 when more than 500 cases per 100,000 residents are registered in the past 28 days.

All three nations moved up from Level 3.

Last week, the CDC put Italy’s neighbor, France, at Level 4 – along with six other destinations. France remains at Level 4 this week.

European surge and Omicron

Italy’s move to Level 4 comes as Europe continue to grapple with another surge in Covid-19 cases.

The Italian government approved an extension of a state of emergency in the country until March 31, according to a news release from the government Tuesday.

The state of emergency gives the government led by Prime Minister Mario Draghi the power to implement measures aiming at containing the coronavirus, including limiting some activity only to those fully vaccinated.

Italy will also impose a five-day quarantine for unvaccinated travelers entering the country, including those coming from the European Union. Those that are vaccinated will also need to provide a negative test result. Those new measures are set to be implemented from December 16 to January 31.

The United Kingdom is facing a “tidal wave” of infections from the new Omicron coronavirus variant, ministers have warned, noting rapid transmission rates in London and across the country. And Germany is also grappling with its fourth wave on the pandemic and a sharp rise in deaths. Both of those nations are also on the CDC’s Level 4 list.

Some Christmas markets in Europe are still planning to operate, but others, including the Munich market, have been canceled.

Meanwhile, the entire world continues to monitor Omicron.

First announced by South African health authorities in late November, the variant has prompted various travel bans on nations in southern Africa. The CDC moved seven southern African nations to Level 4 on November 27 specifically because of Omicron (an eighth nation, Botswana, was already at Level 4). All of those nations remained at Level 4 on Monday.

And the United States implemented tighter travel rules on December 6 because of concern about the variant.

Other nations on Level 4

While Europe is being hard hit, it isn’t the only region with popular tourist destinations on Level 4. Among the other places also considered at “very high” risk for travel are:

• Barbados
• Belize
• Cayman Islands
• Jordan
• Seychelles Islands
• Turkey

In all, more than 80 countries were rated Level 4 as of December 13.

You can view the CDC’s risk levels for global destinations on its travel recommendations page.

Happening on Level 3

Tourists wearing face masks view from an observation deck at the Kuala Lumpur Tower in Kuala Lumpur, Malaysia.

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 – just saw one new addition on Monday.

For Malaysia, the move to Level 3 was good news as it had been residing at Level 4 since June 2021.

Quite a few Caribbean nations popular with Americans seeking warmer climes are currently on Level 3. They include, among others:

• Aruba
• Dominican Republic
• Saint Kitts and Nevis

Also notable: The CDC puts cruise ships, whether at sea or in rivers, at Level 3.

Travelers with international plans have a lot consider here at the holidays, CNN Medical Analyst Dr. Leana Wen recently told CNN Travel.

“This is a very dynamic situation, and travelers should consider how important the trip is to them and have a plan B and a plan C,” said Wen, an emergency physician and professor of health policy and management at the George Washington University Milken Institute School of Public Health.

“They should think through all the scenarios for what could happen. Let’s say that they end up in a country that is now going to implement a mandatory quarantine on arrival. How will they cope with that? Is it worth going?”

US embassies provide country-specific information for American citizens, including whether tests in a particular destination are reliably available within the one-day period required for their return.

Level 2, Level 1 and unknowns

Jamaica, homes to colorful corals reefs, has been moved to Level 2 by the CDC.

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. Three nations moved there Monday. They are:

• Jamaica
• Philippines
• Republic of Congo

This was an improvement for all three nations, which had previously been at Level 3.

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. Only one new nation joined this level on Monday, that of the small African nation of Equatorial Guinea. It previously had been on Level 2.

Finally, there are destinations for which the CDC has an “unknown” risk because of a lack of information. As of December 13, some of those places included:

• Cambodia
• Canary Islands
• Gibraltar
• Nicaragua
• Tanzania

The CDC cautions even fully vaccinated travelers about venturing to destinations with no reliable statistics about the current Covid-19 situation.

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.

Top image: Christmas trees are seen in Trieste, Italy, on December 12. (Photo by Manuel Romano/NurPhoto via Getty Images)

CNN’s Marnie Hunter, Livia Borghese and Rob Picheta contributed to this report.