The designation, now known as "Level 4: Special Circumstances/Do Not Travel," warns travelers to avoid all nonessential travel to the countries and urges vaccinations in the event travel is required, the CDC's website said.

More than 100 locations, including Australia, Canada, France and the U.K., are still listed at the agency's "Level 3: COVID-19 High" warning.

"Make sure you are up to date with your COVID-19 vaccines before traveling to these destinations. If you are not up to date with your COVID-19 vaccines, avoid travel to these destinations," the advisory for that level said.

Many of the Level 3 locations were listed as Level 4 as recently as Sunday. At that time, the level was known as "Level 4: COVID-19 Very High."

But last week, the agency announced that it would reserve "Level 4" warnings "for special circumstances, such as rapidly escalating case trajectory or extremely high case counts, emergence of a new variant of concern, or healthcare infrastructure collapse," according to a statement.