The State Department warned on Thursday that Americans who are traveling abroad "should make contingency plans" as countries around the globe grapple with rising numbers of COVID-19 cases spurred by the omicron variant.
"U.S. citizens who do choose to travel internationally should make contingency plans, as they may have to remain in a foreign country longer than originally planned, which will be at their own expense," the department said in a media note.
"The Department recommends international travel insurance with coverage for COVID-related trip cancellation and medical benefits," it added.
The State Department also noted that for Americans ages 2 years and older coming back into the U.S. from international travel would need either proof of recovery from COVID-19 or a negative COVID-19 test taken within one day before they are set to return.
Other foreign governments may also have additional COVID-19 guidance for visitors upon entering the country, the State Department added.
The guidance underscores the seriousness with which officials are approaching the new omicron variant, the spread of which has already caused staff shortages and reductions in certain services in the United States.
Health officials say the variant, first discovered only a month ago in South Africa, is highly transmissible, but early data also suggests it may not be as severe as delta for people who are vaccinated.
"We know now, incontrovertibly, that this is a highly, highly transmissible virus. We know that from the numbers we're seeing," Anthony Fauci, President Biden's chief medical adviser, said during a White House briefing on Wednesday, adding "all indications point to a lesser severity of omicron versus delta."
A South African study that analyzed a hospital system in the "epicenter" of the new variant said omicron appeared to have already had its peak and did not seem to cause a corresponding spike in hospitalization and deaths.