What ‘100 Percent Effective’ Means for That Ebola Vaccine

Analysis
WIRED.COM by Katie M. Palmer                                                            Aug. 4, 2015

Last week, the medical journal the Lancet published preliminary results on the efficacy of an Ebola vaccine in Guinea, and everybody got really excited—especially about one particular figure. The vaccine, the results suggested, was 100 percent effective at protecting against Ebola, a thrilling prospect in the face of an epidemic that has killed more than 11,000 people. ...

But that number probably means less than you think it does. It’s based on incomplete data, so it doesn’t have the statistical clout it should. And it never will. Based on the vaccine’s early success, the trial’s runners decided that all participants in the study should get it immediately after exposure. That’s a perfectly reasonable, humane reaction, but it also means that the researchers will never be able to collect better data on the vaccine’s efficacy, which is what regulators look for when they’re deciding to approve a drug. In other words, the vaccine’s early success could make it harder for people to get it down the line.

The main thing that makes the new vaccine, rVSV-ZEBOV, seem so great? There’s simply nothing else available. Trials of Ebola vaccines have been almost impossibly difficult to pull off. ... “It’s a high-risk thing to take on a large scale vaccine trial,” says Anne Schuchat, director of the CDC’s National Center for Immunization and Respiratory Diseases. “It usually takes a few years to lay the groundwork....”

Read complete story.
http://www.wired.com/2015/08/100-percent-effective-means-ebola-vaccine/