The U.S. Centers for Disease Control and Prevention (CDC) has just updated its travel advisories levels for several countries around the globe, essentially offering warnings about where COVID-19 risk is currently the highest.

This week, the list of destinations designated Level 4 grew once again, with Armenia, Austria, Barbados, Croatia, Latvia and New Caledonia being bumped up to the agency’s highest travel alert level due to “Very High” incidence of COVID-19 infection. Americans are warned that they should “avoid travel” to countries in this category.

Other nations’ alert statuses were downgraded from Level 4 to Level 3, meaning they’ve been relabeled as having a “High” incidence of COVID-19 and the CDC’s recommendation is to “make sure you are fully vaccinated” before traveling to any of these countries. Argentina, France, Iceland, Lesotho, Morocco, Nepal, Portugal and South Africa were all de-escalated to Level 3 this week.

There are now more than 80 countries on the Level 4 “avoid travel” list, including places that are typically popular among U.S. travelers, such as Jamaica, the Bahamas, St. Kitts and Nevis, Puerto Rico, the, Maldives, Greece, the UK, and Ireland.

USA Today pointed out that the CDC’s travel alerts, like the travel advisories issued by the U.S. State Department, are intended to serve as informed recommendations, not official restrictions. Americans can still decide to visit these countries, subject to any restrictions set by the destination, but do so at their own risk.

Take note that even returning residents attempting to enter the U.S. must provide negative results from a COVID-19 test taken within 72 hours of boarding their flight.

The CDC is actively monitoring health threats around the world on a continual basis. Its four-level system for Travel Health Notices (THNs) reflects the COVID-19 incidence rates or case counts in each country, and advisory levels primarily correspond to each destination’s number of new cases and new-case trajectory (whether daily new cases are increasing, decreasing or remaining stable).

The agency will raise a destination’s THN level when case counts increase and testing metrics surpass certain thresholds and remain above it for 14 consecutive days. Similarly, the CDC lowers a country’s THN level when the incidence rate (or case count) and testing metrics fall below a predetermined threshold and remain so for 28 consecutive days.

Destinations categorized as Level 4 have reported 500 or more new cases per 100,000 people over the preceding 28-day period, while Level 3 countries have seen 100–500 per 100,000 in the past 28 days.