In response to a fast-moving Ebola outbreak, the Trump administration has imposed a U.S. entry ban on foreign travelers who have been in the Democratic Republic of the Congo, Uganda, or South Sudan in the past 21 days, according to a new order issued by the Centers for Disease Control and Prevention.

The order, aimed at preventing the introduction of Ebola cases into the United States, applies to anyone who was in those countries during in recent weeks, irrespective of their nationality of origin, with the exception of American citizens and members of the Army, as well as anyone specifically exempted from the ban by the Department of Homeland Security.

The order, signed by Jay Bhattacharya, the director of the National Institutes of Health who is also serving as a top CDC official, is in effect for 30 days for now.

This is the first time the U.S. has imposed a travel ban in response to an Ebola outbreak.

In the past, officials have relied on a containment strategy that has included enhanced screening of travelers at ports of entry, as was the case during the 2018-2019 Ebola outbreak during President Trump’s first term. At the time, the CDC coordinated a combination of exit screenings of personnel leaving affected areas and further checks at airports.