A U.S. government-backed clinical trial in Liberia showed that two Ebola vaccine candidates were capable of eliciting an immune response after one month of initial vaccination that lasts for at least one year.
Results from the large randomized, placebo-controlled Prevail clinical trial also showed the vaccines did not pose any major safety concerns.
The trials were a conducted by a U.S.-Liberia clinical research collaboration, known as the Partnership for Research on Ebola Virus in Liberia, that included 1,500 adults.
Originally designed to enroll 28,000 volunteers, the trial was scaled back to a phase 2 study when the decline in new Ebola cases made it impossible to conduct a larger study.
The trial was sponsored by the National Institute of Allergy and Infectious Diseases, or NIAID, part of the U.S. National Institutes of Health.
The vaccine candidates included cAd3-EBOZ, co-developed by NIAID's Vaccine Research Center and GlaxoSmithKline plc, and rVSV-ZEBOV, which was initially engineered by scientists from the Public Health Agency of Canada and is now licensed to Merck & Co. Inc.
After one month, 71% of cAd3-EBOZ recipients and 84% of rVSV-ZEBOV recipients developed an antibody response compared to 3% of placebo recipients. After a year, antibody responses stood at 64% in cAd3-EBOZ recipients and 80% in rVSV-ZEBOV recipients.
Investigators also found unexpectedly that the proportion of participants developing malaria by one year was lower for participants who received the investigational vaccines as compared with those receiving placebo, particularly among the rVSV-ZEBOV recipients.