Ebola vaccines prove safe for 600

Phase two of the Ebola vaccine study in Liberia otherwise known as PREVAIL (Partnership for Research on Ebola Vaccines in Liberia) has achieved and exceeded its initial goal of enrolling 600 people, according to leaders of the Liberian-U.S. research team. 

According to a press release, when an independent monitoring group recently reviewed the interim study data on the first 600 people enrolled, they found no major safety concerns related to either of the two study vaccines.  

“We thank the Liberian-U.S. clinical research team conducting this study for their excellent work as well as the many hundreds of Liberians who stepped up to participate and contribute to this critical milestone,” noted Dr. Francis N. Kateh, Deputy Manager for Medical Affairs and Planning, Liberia’s Incident Management System (IMS).

The Data and Safety Monitoring Board (DSMB) commended the team’s accomplishment and said the information collected on the safety of the vaccines support the goal of advancing to the larger Phase 3 trial.

PREVAIL, which opened at Redemption Hospital in Monrovia on February 2, is evaluating a single injection of either of two candidate Ebola vaccines—ChAd3-EBO-Z, made by GlaxoSmithKline, or VSV-ZEBOV, made by NewLink Genetics/Merck—versus a saltwater placebo injection.  

Participants are assigned at random to one of the three groups.  Neither the participants nor the study staff knows who receives the vaccines or placebo.  This study design–randomized, double-blind and placebo-controlled–is considered the “gold standard” for determining whether a medical intervention is safe and effective. 

The release said the phase two portion of the study sought to enroll at least 600 people and follow them closely to find out whether the vaccines were safe and could elicit an immune response before proceeding to Phase 3.  Enrollment in PREVAIL has been steady after intensive engagement with the home communities of the volunteers. As the protocol specifies, after reaching 600, the study has continued to enroll participants.  

The next (Phase 3) component of the study planned to enroll about 27,000 Liberians at risk of Ebola virus infection.  However, as a result of Liberia’s successful infection control and prevention strategy targeting Ebola, there has been only one new case in the country since February 19th. Therefore, together with the DSMB, the PREVAIL leaders—Drs. Stephen Kennedy and Fatorma Bolay, the Liberian co-principal investigators, and Dr. H. Clifford Lane, Deputy Director for Clinical Research at the National Institute of Allergy and Infectious Diseases, U.S. National Institutes of Health—have decided that it is scientifically appropriate to develop additional vaccine sites in other countries in West Africa to consider co-sharing the Phase 3 study. Discussions are currently under way to explore that possibility.  

“Achieving a marked decline in new Ebola cases approaching zero is a wonderful achievement for our country,” noted Dr. Kennedy.  “However, with so few Ebola infections occurring in Liberia, a Phase 3 study here, at this point, would be unable scientifically to put the efficacy of the vaccines to a rigorous litmus test.” 

The Liberian-U.S. research team is evaluating the best way to move forward to contribute to Ebola-directed scientific efforts in West Africa.