Two experimental Ebola vaccines against the Ebola virus have shown promise in protecting against the haemorrhagic fever for at least a year, researchers reported. The findings are based on a study of 1,500 adults that began during the West Africa Ebola outbreak.
In a phase II, placebo-controlled trial conducted in Liberia, both Ebola vaccines generated immune responses that lasted for 12 months without any safety concerns, according to H. Clifford Lane, MD, of the National Institute of Allergy and Infectious Diseases in Bethesda, Maryland, and colleagues.
“This clinical trial has yielded valuable information that is essential for the continued development of these two Ebola vaccine candidates and also demonstrates that well- designed, ethically sound clinical research can be conducted during an epidemic,” said Anthony S Fauci, Director of the US National Institute of Allergy and Infectious Diseases (NIAID).
The study looked at 1,500 patients in Liberia, and took place amid and after the outbreak of Ebola in Liberia from 2014 into 2015. The patients were divided at random into three groups of 500 each. One group received one test vaccine, the second group the other test vaccine, and the third group received a placebo (saltwater injection). It was important to include the placebo so that the research team could, compare how well the test vaccines worked.
The study team tested each of these samples for infection-fighting antibodies against the Ebola virus. After one week, only modest levels of antibodies were seen with both vaccines. However, by one month, 71 percent of cAd3-EBOZ recipients and 84 percent of rVSV-ZEBOV recipients developed an antibody response compared with three percent of placebo recipients.
At one year, the antibody responses were largely maintained in both groups: 64 percent of cAd3-EBOZ recipients and 80 percent of rVSV-ZEBOV recipients had antibody response compared with seven percent of placebo recipients.
Researchers 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.
The trial was conducted as part of a US-Liberia clinical research collaboration known as the Partnership for Research on Ebola Virus in Liberia (PREVAIL). Future studies are needed to determine if this is a chance finding or if it has some significance related to cross-reactive immunity. The study was published in the New England Journal of Medicine.