Ebola Test Vaccines Produce One Year Immune Response

Dr. Fatorma Bolay, Co-Principal Investigator.

Dr. Fatorma Bolay, co-principal investigator of the joint clinical research partnership between the Liberian and U. S. governments through the Ministry of Health of Liberia and the US National Institutes of Health, says PREVAIL 1 results have shown that the two test vaccines, cAd3-EBOZ, and rVSV-ZEBOV, pose no major safety concerns and can produce immune responses within one month after vaccination that lasts for at least one year.

He said the results were published in the October 12th issue of the prestigious New England Journal of Medicine.

Speaking at the MICAT regular press briefing  in Monrovia recently, Dr. Bolay quoted his co-principal investigator on the study, Dr. Stephen Kennedy, saying, “by developing research capacity and infrastructure to answer questions about Ebola and other infectious diseases that are threats to global health, PREVAIL has become a successful model for the implementation of clinical trials during health outbreaks in resource-constrained environments.”

He expressed gratitude to the thousands of Liberian volunteers who enrolled in the study, on behalf of his other co-leader – in addition to Dr. Kennedy and Dr. H. Clifford Lane, the Deputy Director for Clinical Research and Special Projects at the National Institute of Allergy and Infectious Diseases (NIAID) – part of the US National Institutes of Health (NIH) that sponsored the study in collaboration with the Liberian Ministry of Health.

“More than 98 percent of those who enrolled returned for their follow-up visits during the year. The study was a true collaboration with the people of Liberia who participated and made it a success,” Dr. Bolay said.

He noted that the PREVAIL I study will follow, for several years, those who enrolled in the study, to determine the long-term benefits of the vaccines. “At PREVAIL, we are doing our best to make an impact on the global public health through clinical research. As Tolbert Nyenswah (Director General of the National Public Health Institute of Liberia) noted recently, and I quote, ‘We cannot succeed in the fight against Ebola unless we identify primary prevention tools.’ Through PREVAIL, we are developing vaccines and therapeutics in our region that can help Liberians and the rest of the world.”

He said the cAd3-EBOZ vaccine candidate was co-developed by NIAID’s Vaccine Research Center and GlaxoSmithKline (GSK), while rVSV-ZEBOV, initially engineered by scientists from the Public Health Agency of Canada, is now licensed to Merck Sharp & Dohme Corp., a subsidiary of Merck & Co. GSK. Merck provided the test vaccines for the study.

PREVAIL 1 was the first large-scale Ebola study conducted in Liberia. Between February 2 and April 30, 2015, 1,500 men and women ages 18 and older were enrolled in the study at Redemption Hospital in New Kru Town, Monrovia. People who enrolled in the study had no reported history of the Ebola virus disease. The participants were divided at random into three groups of 500 each.

Emmanuel Lansana, first vaccine volunteer

One group received one test vaccine, the second group the other, while the third group received a placebo or saltwater injection. “It was important to include the placebo so that our research team could compare how well the test vaccines worked,” he said.

The study was originally designed to enroll 27,000 volunteers to see whether the vaccines could prevent the Ebola virus disease. However, it had to be scaled back to be much smaller when the decline in new Ebola cases made it impossible to conduct the larger study.

Participants gave blood samples before vaccination and again at one week, one month, six months, and one-year post-vaccination. 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.

Emmanuel Lansana, the first vaccine participant or volunteer, explained that after his inoculation with the Ebola vaccine on February 2, he experienced great resentment from his wife and other family members. According to Lansana, he was undaunted by their reactions because he was poised to contribute to the global public health effort in the development of a cure for Ebola.


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