BETHESDA, Maryland, March 26, 2015 (ENS) – Two experimental Ebola vaccines appear to be safe based on their evaluation in more than 600 volunteers who participated in the first stage of the Partnership for Research on Ebola Vaccines in Liberia (PREVAIL) Phase 2/3 clinical trial.
Based on these findings, the study, sponsored by the U.S. National Institute of Allergy and Infectious Diseases, NIAID, which is part of the National Institutes of Health, may now advance to Phase 3 testing.
The vaccine safety findings are based on reviews of the trials by an independent Data and Safety Monitoring Board, required by the National Institutes of Health for all NIH-supported or conducted multi-site clinical trials that entail potential risk to the participants.
“We are grateful to the Liberian people who volunteered for this important clinical trial and encouraged by the study results seen with the two investigational Ebola vaccine candidates,” said NIAID Director Dr. Anthony Fauci.
“Now we must move forward to adapt and expand the study so that ultimately we can determine whether these experimental vaccines can protect against Ebola virus disease and therefore be used in future Ebola outbreaks,” he said.
The PREVAIL trial, which began on February 2 in Monrovia, Liberia, is testing the safety and efficacy of two vaccines – the cAd3-EBOZ candidate vaccine co-developed by NIAID scientists and GlaxoSmithKline, and the VSV-ZEBOV candidate vaccine developed by the Public Health Agency of Canada and licensed to NewLink Genetics Corporation and Merck.
Volunteers are assigned at random to receive a single injection of one or the other vaccine, or a placebo injection of a saline solution.
The clinical trials are double-blind, meaning that neither the volunteers nor staff know whether a vaccine or placebo was administered. A randomized, double-blind, placebo-controlled trial is considered the gold standard in clinical research.
While the initial enrollment goal in the Phase 2 study has been met and the vaccines proven safe, the researchers are continuing Phase 2 study enrollment at Redemption Hospital in Monrovia through late April 2015.
This would boost enrollment in the Phase 2 portion of the trial to 1,500 people and would be done, in part, to increase the percentage of women in the study for a more robust data set. Currently, women make up about 16 percent of the clinical trial volunteers.
The study follow-up period is planned to be at least one year, during which two additional blood samples would be obtained from all volunteers at six and 12 months post-vaccination to determine the durability of the immune responses.
These proposed changes will be discussed with the U.S. Food and Drug Administration and are under review by the institutional review boards in Liberia and the United States, Dr. Fauci explained.
One year after the current outbreak of the Ebola virus in West Africa, the disease has sickened about 24,000 people and claimed more than 10,000 lives.
Investigators had planned to enroll 27,000 people in Liberia at risk of Ebola infection in the Phase 3 portion of the trial. However, there has been only one new confirmed case of Ebola infection in the country since February 19.
Given this decline in Ebola infection incidence, the trial leaders – H. Clifford Lane, M.D., NIAID deputy director for clinical research, and Liberian co-principal investigators Stephen Kennedy, M.D., and Fatorma Bolay, Ph.D. – have determined that it is scientifically appropriate to expand the trial to additional sites in other West African countries.
Discussions are underway to explore that possibility.
The Liberia-U.S. research team also plans to launch a separate natural history study of Ebola survivors to better understand the after-effects of Ebola virus disease.
Four sites in Monrovia, Liberia and locations in the United States may begin enrollment into this study in the coming months, pending regulatory review and approval.