(CNN) — The US Centers for Disease Control and Prevention packed in another four entries to its growing list of highest-risk destinations for travel on Tuesday, including multicultural Malaysia.
The CDC places a destination at "Level 4: Covid-19 Very High" risk when more than 500 cases per 100,000 residents are registered in the past 28 days.
Before the pandemic, Malaysia was a travel hot spot, renowned for its beaches, cuisine, mix of cultures and the cosmopolitan capital of Kuala Lumpur.
The four destinations added to Level 4 on February 22 were:
All four destinations were previously at "Level 3: Covid-19 High" risk last week.
Level 4, the CDC's highest, has now swelled to more than 140 places, illustrating the vast range and rapid spread of the Omicron variant around the world this year. In early January, there were around 80 destinations listed there.
Level 4 now has more destinations than all the other CDC categories combined.
CDC: Avoid Level 4 destinations
Mexico has been one of the easiest places to visit throughout the pandemic, but it's now at Level 4. Pictured: People enjoy the beach in Cancun on October 8, 2020.
Pedro Pardo/AFP via Getty Images
The CDC advises travelers to avoid vacations to Level 4 countries. CDC thresholds for travel health notices are based primarily on the number of Covid-19 cases in a destination.
The CDC does not include the United States in its list of advisories, but it was color-coded at Level 4 on February 22 on the agency's map of travel risk levels.
Last week, South Korea and French Polynesia were among the destinations added to Level 4.
Other tourist favorites stalled on Level 4 even longer include Mexico, Canada, France, Peru, Singapore and Spain. The United Kingdom has been there since July 2021.
In its broader travel guidance, the CDC has recommended avoiding all international travel until you are fully vaccinated.
South Korea moved to Level 4 on February 14. Here, visitors pose for photos at Gyeongbokgung Palace in Seoul on July 3, 2020.
ED JONES/AFP/AFP via Getty Images
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 are entering 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 in mid-February.
"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."
Changes at Level 3
New Zealand, which rode out much of the pandemic in near isolation with relatively few infections, was moved up to "Level 3: Covid-19 High" risk. It had previously been at "Level 2: Covid-19 Moderate" risk.
The Level 3 "high" risk category -- which applies to destinations that have had between 100 and 500 cases per 100,000 residents in the past 28 days -- saw three total additions on Tuesday. They were:
• New Zealand
The move was good news for Namibia, a desert nation in southwest Africa. It had previously been at Level 4. The small, isolated nation of Timor-Leste, which shares one island with Indonesia in its vast archipelago, moved up from Level 1.
Levels 2, 1 and unknown
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. On Tuesday, the CDC moved safari favorite Kenya to Level 2. It previously had been at Level 3. Currently, the CDC's Level 2 is a lonely place with just four destinations in the category.
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. No new destinations were moved to Level 1 on Tuesday. There are currently only five destinations in the category. That includes China, which just hosted the Winter Olympic Games.
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 addition to this category: the Madeira Islands, a Portuguese territory in the North Atlantic.
Tanzania, Cambodia and Macau 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 cruise ship waits for people to embark before leaving PortMiami on December 31, 2021, in Miami, Florida.
Joe Raedle/Getty Images
On February 15, the CDC lowered the risk level for cruise travel from Level 4 to Level 3, where it remained on February 22.
The Level 3 designation urges travelers to "make sure you are up to date with your Covid-19 vaccines before cruise ship travel."
The agency still advises avoiding cruise travel if you are not up to date with your vaccines or if you are up to date but at increased risk for severe illness from Covid-19.
For cruise travel, the CDC's primary criteria in evaluating the risk level is the number of new Covid-19 cases among crew and the case trajectory among crew over the past 14 days.
Level 4 means more than 2,000 cases detected among crew on cruise ships over the past 14 days. Level 3 is 1,000 to 2,000 news cases. Level 2 is 500-999 new cases and Level 1 is fewer than 500 new crew cases.
More considerations for travel
Transmission rates are important to consider when making travel decisions, but there are other factors to weigh as well, 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.
"People who are unvaccinated remain at high risk and really should not be traveling at this point," she said.
People should be wearing a high-quality mask -- N95, KN95 or KF94 -- anytime they're in crowded indoor settings with people of unknown vaccination status, she 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?