The United Nations, led by Secretary-General Ban Ki-moon, has launched a coordinated effort to help Guinea, Liberia, Nigeria, and Sierra Leone stop the spread of Ebola, which has killed more than 1,000 people and is now affecting more than 1 million people, according to UN.org.

The efforts got a major boost last week when Dr. David Nabarro, British physician and public health expert, was appointed senior U.N. system coordinator for Ebola to support the work done by World Health Organization. The agency has since said the outbreak is a “public health emergency of international concern.”

What does that mean?

In a UN.org interview and video, Nabarro said that means “trying to find people who are infected, putting some kind of restrictions on their movements so they cannot travel to infect other people, and also containing them in locations where they can get proper treatment and support but, at the same time, stop them from moving to places and transmitting the virus to others. That’s the basis of the efforts to prevent spread.

“Now of course that does not mean that you stop all people from traveling from the affected countries. It also does not mean that you stop all travel to the affected countries. It’s focusing on the people who themselves are likely to have the disease or to have been exposed to the disease. They’re the ones who we try to prevent from moving and also who become part of the area of containment when the outbreak is present.”