A large clinical trial to assess the safety and efficacy of two experimental vaccines to prevent Ebola virus infection has begun in Liberia. The trial is being led by a recently formed Liberia-U.S. clinical research partnership and is sponsored by the NIH’s National Institute of Allergy and Infectious Diseases (NIAID). The Partnership for Research on Ebola Vaccines in Liberia or PREVAIL, a Phase 2-3 study, is designed to enroll approximately 27,000 healthy men and women aged 18 years and older.
Image courtesy of NIAID
One vaccine candidate, cAd3-EBOZ, uses a chimpanzee-derived cold virus to deliver genetic material from the Zaire Ebola strain, which dominated in Liberia. Published interim results from a Phase 1 trial of this vaccine, which was co-developed by NIAID scientists and GlaxoSmithKline, provided necessary safety information and showed that it prompted immune responses to the outer coat of Ebola virus.
The other candidate, VSV-ZEBOV, employs vesicular stomatitis virus, an animal microbe that primarily affects cattle, to carry an Ebola virus gene segment. The VSV-ZEBOV vaccine was developed by the Public Health Agency of Canada and licensed to NewLink Genetics Corporation through its wholly owned subsidiary BioProtection Systems Corporation. Phase 1 trial results of this vaccine also provided safety information and showed that it prompted immune responses to the outer coat of Ebola virus. These results have not yet been published but were made available to the regulatory bodies reviewing the study.
"The scale of the current Ebola outbreak in West Africa is unprecedented, and specific medical countermeasures are needed for this and future outbreaks," said NIAID Director Dr. Anthony S. Fauci. "It is imperative that any potential countermeasures, including vaccines, be tested in a manner that conforms to the highest ethical and safety standards in clinical trials designed to provide a clear answer to the question of whether a candidate vaccine is safe and can prevent infection."
Trial participants will be divided into three equal-sized groups that will receive either a placebo or one of the two vaccines. The trial will be double-blinded so that neither subjects nor staff will know if a vaccine or placebo was administered. The study is expected to last about 12 months.