Stop travel to and from the affected countries.
That won’t work because people can travel to other non infected countries first and then come here. The borders between some of these African countries are very lax. So, say you are a Chinese national working in one of these countries. You cross the border where there is lax attention or where you can pay a bribe to cross. Then you take a flight home to China and then from there to the USA.
You might not have gotten an entry stamp in you passport going into one of the affected countries nor an exit stamp when you left. So you are bureaucratically entering the US from a China.