Six early-stage trials of an experimental Ebola vaccine have found that it appears to be safe and triggered robust production of Ebola-fighting antibodies, scientists reported Wednesday.
Since trials cannot ethically expose volunteers to Ebola, the production of antibodies is a proxy for whether vaccines could prevent or even treat the disease.
There is currently no vaccine or specific treatment for Ebola, which has killed over 10,000 people in West Africa since last spring, according to the World Health Organization. It is the worst Ebola epidemic in history, but it finally appears to be abating.
The trials — two in the United States and four in Africa and Europe — all tested a vaccine called VSV-ZEBOV, which was developed at the Public Health Agency of Canada and licensed to NewLink Genetics Corp. and then to Merck & Co. Inc. It consists of a cattle virus called rVSV that has been engineered to carry Ebola genes, which produce proteins meant to trigger production of anti-Ebola antibodies.
According to separate teams of scientists, that is what happened, two papers in the New England Journal of Medicine reported.
In the U.S. trials, conducted independently but cooperatively at the National Institutes of Health and the Walter Reed Army Institute of Research starting last October, 52 healthy adult volunteers received single injections of saline or either of two doses of vaccine.
The most common side effects were mild, such as pain at the injection site and short-lived fever. All 40 participants who received vaccine produced anti-Ebola antibodies within 28 days, with most responding sooner.
The higher dose triggered triple the antibody response of the lower dose. The "robust'' response to a single dose "could be particularly useful in outbreak interventions,'' said Walter Reed's Col. Stephen Thomas, senior author of the U.S. paper.
The higher dose is being tested in a larger trial in Liberia. Partly through that trial, both VSV-ZEBOV and an experimental vaccine from GlaxoSmithKline PLC called cAd3-EBOZ "appear to be safe,'' NIH announced last week.
The other studies were similarly encouraging.
In coordinated trials in Germany, Switzerland, Gabon and Kenya, 158 healthy volunteers received a placebo or any of five dose-levels of VSV-ZEBOV vaccine.
Although the Geneva study was temporarily halted last year after 11 of 51 participants developed arthritis, overall there were "no serious vaccine-related adverse events,'' the researchers reported. All 150 people who received vaccine developed antibodies to Ebola, with higher responses to higher doses.