Secret serum likely saved Ebola patients

(CNN) — Three top secret, experimental vials stored at subzero temperatures were flown into Liberia last week in a last-ditch effort to save the American missionary workers who had contracted Ebola, according to a source familiar with details of the treatment.

A representative from the National Institutes of Health contacted Samaritan's Purse, the aid organization both Dr. Kent Brantly and Nancy Writebol worked for in Liberia, and offered up the experimental treatment, known as ZMapp, according to the source.

The drug was developed by the biotech firm Mapp Biopharmaceutical Inc. The patients were told that this treatment had never been tried before in a human being, but had shown promise in small experiments with monkeys.

According to company documents, four monkeys infected with Ebola and then given the therapy within 24 hours had survived. Two of four monkeys that started therapy within 48 hours also survived, while one that was not treated died within five days of exposure.