Two Experimental Ebola Vaccines Show Promise in Phase 2 Trial

Two investigational vaccines showed promise to protect against Ebola virus disease (EVD), according to data from the phase 2 Partnership for Research on Ebola Vaccines in Liberia (PREVAIL 1) trial.

Fatorma Bolay, PhD, from the Liberian Institute for Biomedical Research in Monrovia, and colleagues presented the results of their study at the 2016 annual Conference on Retroviruses and Opportunistic Infections, held February 22 to 25, in Boston, Massachusetts.

In November 2014—during the West African Ebola outbreak—2 candidate Ebola virus vaccines were in late phase 1 testing, the authors state in the conference abstract. These were the chimpanzee adenovirus 3 (cAd3-EBOZ)-based vaccine and the recombinant vesicular stomatitis virus (rVSV-ZEBOV)-based vaccine. PREVAIL 1 was originally designed as a phase 3 trial that aimed to evaluate these vaccines in more than 28,000 participants. However, because of declining numbers of new cases of EVD, a phase 3 trial was no longer feasible, and the study was instead converted to a phase 2 safety and immunogenicity trial.

The study was conducted in Monrovia, Liberia, from February through April, 2015. It enrolled 1,500 volunteers aged 18 and older who were randomized into one of 3 groups, and received either one of the 2 vaccines or a saline injection (placebo). The researchers aimed to compare antibody responses, targeted symptoms, and the occurrence of injections site reactions among the 3 groups.

The results showed that the 2 vaccines were well tolerated. The incidence of targeted symptoms (including headache, muscle pain, fever, and fatigue), injection site reactions, and lymphocyte counts differed between the 2 vaccine groups and the placebo group after one week, but not after one month.

The 2 vaccines also induced an immune response. After one month, 87% of participants in the cAd3-EBOZ vaccine group, and 94% of those in the rVSV-ZEBOV vaccine group, had developed a measurable antibody response to Ebola virus.

The results of this study demonstrate that, “it is possible to conduct a well-designed, randomized, placebo-controlled trial in the middle of an epidemic outbreak,” the researchers emphasize. “Both vaccines were demonstrated to be safe and immunogenic,” they conclude.

Dr. Parry graduated from the University of Liverpool, England in 1997 and is a board-certified veterinary pathologist. After 13 years working in academia, she founded Midwest Veterinary Pathology, LLC where she now works as a private consultant. She is passionate about veterinary education and serves on the Indiana Veterinary Medical Association’s Continuing Education Committee. She regularly writes continuing education articles for veterinary organizations and journals, and has also served on the American College of Veterinary Pathologists’ Examination Committee and Education Committee.