Two Ebola Vaccines Yield Positive Results in Clinical Trial in Liberia

In a step toward a life-saving vaccine for Ebola virus disease, 2 test vaccines have been found to be safe and effective at inducing long-lasting immunity against the virus in a study of 1500 adults in Liberia.

Responsible for a devastating outbreak in 2014-2016 in many countries in Africa, the Ebola virus is transmitted via direct contact with blood or bodily fluids of an infected individual or someone who has died from the disease, contaminated objects, and possibly through sexual contact with a man who has recently recovered from the infection, according to the Centers for Disease Control and Prevention (CDC). Symptoms of an Ebola infection, which can occur 2 to 21 days after exposure, include a fever, severe headache, body aches, unexplained hemorrhaging, among other signs. Individuals can recover from the infection with supportive clinical care and a strong immune response and can develop antibodies against the virus that can last for 10 years.

Currently, there are no drugs or vaccines against the Ebola virus; however, during the 2014-2016 outbreak in West Africa, researchers were able to test 2 experimental vaccines. A total of 1500 men and women in Liberia were enrolled in the research. The participants were 18 or older and “had no reported history of Ebola virus,” according to an official article on the results of the trial from the National Institutes of Health (NIH). The research was sponsored by the NIH’s National Institute of Allergy and Infectious Diseases (NIAID) and the full results were published in the New England Journal of Medicine.

After receiving one of the test vaccines, cAd3-EBOZ or rVSV-ZEBOV, or saline placebo, the participants’ immune responses were checked via blood samples. The investigators checked for antibodies to the virus before vaccination, as well as up to 1 year after vaccination.

A total of 4% of the participants had antibodies against Ebola at the beginning of the study, “even though they had no known history of Ebola virus disease,” according to the NIH. Participants showed a modest immune response to the virus 1 week after vaccination with either vaccine. After 1 month, the study results showed that “71% of cAd3-EBOZ recipients and 84% of rVSV-ZEBOV recipients developed an antibody response.” After 1 year, 64% of those who received the cAd3-EBOZ vaccine yielded an antibody response vs 80% of those who received rVSV-ZEBOV. About 7% of the participants who received the saline injection had antibody responses.

No major safety concerns were detected in any of the participants. Those side effects that were reported were temporary and included, “headache, muscle pain, fever, and fatigue,” according to NIH.

According to the NIH, “These findings showed that both test vaccines could produce immune responses by 1 month after vaccination and that the immune response could last for at least 1 year.”