U.S. health officials have changed their advice to international travelers about measles, saying that Americans should be vaccinated against the virus no matter where they're going.

U.S. residents are recommended to get measles-mumps-rubella shots, anyway. But the Centers for Disease Control and Prevention previously emphasized the importance of vaccination for travelers going to countries with outbreaks.

Last week, the CDC updated its guidance to call for vaccinations for travelers going to all other countries.

Ashley Darcy-Mahoney, a researcher at George Washington University's nursing school, called the update significant.

An Colorado outbreak last month stemmed from an international flight that landed in Denver, she noted. The CDC travel notice change reflects a recognition that people are not just being exposed to measles in countries where it's spreading, but also in airplanes and during travel, she added.

“We're seeing a shift from localized outbreaks to transmission in transit,” and the CDC seems to be responding to that, Darcy-Mahoney said.

The travel notice advises two doses for all Americans ages 1 and older. An early dose is advised for traveling infants ages 6 months to 11 months. The U.S. has seen more than 1,000 measles cases so far this year.