In Gupta's optimistic assessment, Brantly's "near complete recovery" began within hours of receiving the treatment that "likely saved his life." Writebol is also reportedly improved since receiving the treatment, known as zMapp. But to say that it was a secret implies a frigid American exceptionalism; that the people of West Africa are dying in droves while a classified cure lies in wait.

The "top-secret serum" is a monoclonal antibody. Administration of monoclonal antibodies is an increasingly common but time-tested approach to eradicating interlopers in the human body. In a basic monoclonal antibody paradigm, scientists infect animals (in this case mice) with a disease, the mice mount an immune response (antibodies to fight the disease), and then the scientists harvest those antibodies and give them to infected humans. It's an especially promising area in cancer treatment.

In this case, the proprietary blend of three monoclonal antibodies known as zMapp had never been tested in humans. It had previously been tested in eight monkeys with Ebola who survived—though all received treatment within 48 hours of being infected. A monkey treated outside of that exposure window did not survive. That means very little is known about the safety and effectiveness of this treatment—so little that outside of extreme circumstances like this, it would not be legal to use. Gupta speculates that the FDA may have allowed it under the compassionate use exemption.

A small 2012 study of monoclonal antibody therapy against Ebola found that it was only effective when administered before or just after exposure to the virus. A 2013 study found that rhesus macaques given an antibody mix called MB-003 within the 48-hour window had a 43 percent chance of surviving—as opposed to their untreated counterparts, whose survival rate was zero.

This Ebola outbreak is the largest in the history of the disease, in terms of both cases and deaths, 729 887 known so far. As Chan warned in her call for urgent international action, the outbreak is geographically the largest, already in four countries with fluid population movement across porous borders and a demonstrated ability to spread by air travel. The outbreak will be stopped by strategic quarantines and preventive education, primarily proper handling of corpses. More than 60 aid workers have become infected, but many more will be needed to stem the tide.

Dr. Anthony Fauci, director of the U.S. National Institute of Allergy and Infectious Disease (NIAID), is encouraged by the antibody treatment.

"Obviously there are plans and enthusiasm to expand this," Fauci told me. "The limiting factor is the extraordinary paucity of treatment regimens." Right now the total amount available, to Fauci's knowledge, is three treatment courses (in addition to what was given to Brantly and Writebol).