A cordon sanitaire won't work. You're betting against the ingenuity of every single person trapped behind it, and the inevitable infected refugees are very motivated to confound efforts to find them.
No, I'm betting the world's medical resources can contain the occasional small outbreak created by the occasional individual who gets past the cordon, particularly since such containment doesn't have to last forever. You can't put out an inferno, but you can put out scattered sparks.
We're talking about a region with more than 20 million people, and recent research indicates that the disease may become endemic rather than burning itself out. Cordons would just hamper our ability to get aid in and try to keep infected patients isolated. What's needed is immediate and large scale increases in the number of isolation beds available in field hospitals, tons of PPE, and trained personnel. Or perhaps we should ignore the consensus of the entire infectious disease and medical communities.
Or perhaps we should ignore the best advice of both the medical and epidemiological communities and throw our effort behind an impossible and inhuman military containment scheme...