“This alignment better reflects the current, unpredictable, and ever-evolving threat posed by covid-19,” the department said in an email. “We continue to strongly recommend U.S. citizens reconsider all travel abroad, and postpone their trips if possible.”

In a media note, the department said the change doesn’t “imply a reassessment of the current health situation in a given country,” but instead indicates a change in the advisory system to rely more heavily on information from the Centers for Disease Control and Prevention.

The note said that in addition to reflecting the travel health notices put out by the CDC, the advisories also consider “logistical factors” such as the availability of in-country testing and travel restrictions for U.S. citizens.

If travelers decide to go to countries that have a Level 4 advisory, the State Department recommends they read travel information about the dangers of visiting high-risk countries.

The upgraded warnings come as the number of U.S. travelers continues to rise and more countries around the world start to open their borders to Americans. On Monday, Greece started to allow U.S. citizens back with a negative coronavirus test or proof of vaccination. And United Airlines announced new flights to Greece, Iceland and Croatia starting in July.

The CDC said earlier this month that fully vaccinated people can travel at low risk. But officials also said they still did not recommend travel because of rising cases in the United States and globally.

On its website, the agency recommends delaying international travel until people are fully vaccinated, but it adds a warning.

“Fully vaccinated travelers are less likely to get and spread covid-19,” the website says. “However, international travel poses additional risks and even fully vaccinated travelers are at increased risk for getting and possibly spreading new COVID-19 variants.”