The United States Centers for Disease Control and Prevention added 16 destinations to its "very high" Covid-19 risk level on Monday.

The "very high risk" travel list or the level 4 risk list of the destination means people should avoid traveling to this destination without being fully vaccinated. 

The 16 new destinations to make up the list include Greece, Ireland, and the US virgin islands.

"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 says.

Destinations that fall into the "very high" risk category have had more than 500 cases per 100,000 residents in the past 28 days, according to CDC parameters.

Andorra, Curaçao, Gibraltar, Greece, Guadeloupe, Iran, Ireland, Isle of Man, Kazakhstan, Lesotho, Libya, Malta, Martinique, Saint Barthelemy, Saint Martin, and US Virgin Islands, are the destinations that moved to level 4 of the travel risk list.

You can look up the CDC's risk level of any destination on its travel recommendations page.