The CDC has issued a travel advisory for Americans traveling to Europe, since measles is making a comeback there. Newsweek reports:

According to the CDC, more than 14,000 cases of the highly infectious virus have so far been detected in Eastern and Western Europe since January 2016. Sixteen countries in Europe—Austria, Belgium, Bulgaria, the Czech Republic, Denmark, France, Germany, Hungary, Iceland, Italy, Portugal, Slovakia, Spain, Sweden, Romania and the U.K.—have all reported cases of the virus.

Measles transmission is highly preventable through routine vaccination. A vaccination for the virus is recommended by the CDC, especially when traveling to locations where recent cases were reported. The CDC recommends getting vaccinated at least four to six weeks before traveling to an affected region of the world in order for the vaccine to be most effective. But vaccination rates are still low in some parts of the world, either due to lack of access or because of personal and religious beliefs.