Federal health authorities issued a warning Monday against travel to several European countries as well as Jordan and Tanzania amid growing fears of the omicron variant, telling people to make sure they are fully vaccinated if they must visit.

The Centers for Disease Control and Prevention said to avoid travel to France, Portugal, Cyprus, Andorra and Liechtenstein, grouping all in a Level 4 category that represents a “very high” level of the coronavirus. Countries and territories in this group have an infection incidence rate of more than 500 new cases per 100,000 people over the past 28 days (or, in places with fewer than 100,000 residents, more than 500 cases cumulatively over the past 28 days).

“Because of the current situation in France, even fully vaccinated travelers may be at risk for getting and spreading COVID-19 variants,” one advisory reads.

Several countries imposed travel restrictions to stop the spread of the omicron variant, but the WHO says the move only works “at the beginning of an outbreak. (Luis Velarde/The Washington Post)

Last week, the CDC urged against travel to Niger, Papua New Guinea, Poland, and Trinidad and Tobago.

The CDC also recently told airlines to share contact information for people entering the United States who have been in southern Africa, where the omicron variant was initially identified. Previously, the CDC had ordered airlines and aircraft operators to collect contact details on passengers and asked that they share it with federal health authorities “upon request,” to aid public health follow-up.

Worries that omicron could prove more transmissible and more resistant to vaccinations have triggered a cascade of travel restrictions around the world. But many experts question the value of travel bans, and the World Health Organization has urged against them.