NEW YORK (AP) — A stepped-up screening program that checks the temperature of travelers arriving from West Africa is starting at New York’s Kennedy International Airport, part of an ongoing effort to stop the spread of Ebola, which has so far killed more than 4,000 people.

The effort to screen travelers from the three West African countries most affected by Ebola starts Saturday at Kennedy and will be expanded over the next week to Newark Liberty, Washington Dulles, Chicago O’Hare and Hartsfield-Jackson in Atlanta.

Customs officials say about 150 people travel daily from or through Liberia, Sierra Leone or Guinea to the United States, and nearly 95 percent of them land first at one of the five airports.

There are no direct flights to the U.S. from the three countries, but Homeland Security officials said last week they can track passengers back to where their trips began, even if they make several stops. Airlines from Morocco, France and Belgium are still flying in and out of West Africa.

President Barack Obama said Wednesday that the new screening measures are “really just belt and suspenders” to support protections already in place. Border Patrol agents already look for people who are obviously ill, as do flight crews, and passengers departing from West Africa are being screened.