Editor's Note — CNN has launched Unlocking the World, a weekly newsletter to guide you through the latest travel developments and more. Sign up here
(CNN) — The US Centers for Disease Control and Prevention added eight destinations to its highest-risk category for travel on Monday, including the world's No. 2 most-visited nation before the pandemic started.
In its weekly update of Covid-19 travel advisories, the CDC advised against travel to tourist favorite Spain at this time. In 2019, Spain received more international visitors than nearly every other nation in the world, except France, according to figures from the UN's World Tourism Organization.
The CDC also added seven more places -- spanning the Caribbean, Africa and the Middle East as well as Europe -- to its "Level 4: Covid-19 Very High" category. They are:
• San Marino
The CDC places a destination at Level 4 when more than 500 cases per 100,000 residents are registered in the past 28 days.
Three tiny destinations in Europe -- Gibraltar, Monaco and San Marino -- provide a cautionary example about traveling to places without reliable statistics. They all shot up to Level 4 on Monday from the CDC's "unknown" risk category. Destinations are put there when there is a lack of reliable information coming from them to the CDC.
Spain, Finland and Lebanon all moved up from Level 3, which is considered "high risk." Spain's designation comes even as it boasts impressive vaccination stats. As of December 17, more than 80% of the population had been fully vaccinated.
The landlocked northern African nation of Chad had previously been at Level 1, the "low risk" category.
Surging cases, Omicron worries and travel bans
Travel to and across Europe is becoming increasingly hard for tourists, particularly those from the United Kingdom, where cases have skyrocketed. France has placed a ban on all nonessential visitors to and from the UK. The Netherlands entered a strict lockdown on Sunday, with nonessential shops, hospitality venues and cultural institutions closing.
The Royal Caribbean cruise ship Symphony of the Seas is seen moored in the Port of Miami on August 1, 2021.
Daniel Slim/AFP/Getty Images
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.
Other nations on Level 4
Spain is hardly alone. Much of Europe is currently ranked at the highest travel risk. Other big travel names already at the CDC's Level 4 include:
• United Kingdom
And Europe isn't the only continent with popular tourist destinations on Level 4. Among the other places also considered at "very high" risk for travel are:
• South Africa
In all, almost 90 countries were rated Level 4 as of December 20.
Level 3 news
A panoramic view of the main square in Cusco, Peru, which has moved up to Level 3.
Ernesto Benavides/AFP/Getty Images
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 two new additions on Monday:
• St. Vincent and the Grenadines
The move was good for the Caribbean island-nation of St. Vincent and the Grenadines, which had been at Level 4. However, it was bad news for South America's Peru, which had been at Level 2 since early October.
Level 2, Level 1 and unknowns
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. It only saw one addition on Monday, that of St. Pierre and Miquelon. The tiny French territory off the coast of Newfoundland, Canada, previously had been at Level 1.
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. It saw no new additions on Monday.
Finally, there are destinations, as cited above, for which the CDC has an "unknown" risk because of a lack of information. On Monday, it added four places to this category:
• Falkland Islands
• French Guiana
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.