Experimental Ebola vaccines elicit year-long immune response

Modesto Morganelli
Ottobre 13, 2017

Results from a large randomised, placebo-controlled clinical trial in Liberia show that two candidate Ebola vaccines pose no major safety concerns and can elicit immune responses by one month after initial vaccination that last for at least one year. The study was done on 1,500 adults across West Africa between February 2, 2015 and April 30, 2015, wherein the outbreak of Ebola has been most prevalent. The National Institute for Allergy and Infectious Diseases (NIAID) sponsored the study while GSK and Merck provided vaccine doses. As per the Director of NIAID, Anthony S. Fauci, these clinical trials have produced valuable details which can be highly beneficial for the continuous development of two Ebola vaccine candidates.

PREVAIL conducts collaborative biomedical research in accordance with best practices, to advance science, strengthen health policy and practice, and improve the health of people in Liberia and around the world. Originally created to enrol 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 large efficacy study. "The work of PREVAIL, ranging from the Ebola vaccine to the Ebola survivor studies, clearly manifest the prospects of such a sustainable partnership and clinical research platform".

One of the vaccine candidate includes cAd3-EBOZ, which was developed by GlaxoSmithKline in association with NIAID's Vaccine Research Center, whereas the other candidate includes rVSV-ZEBOV, which is licensed by Merck Sharp & Dohme Corp, a subsidy of Merck & Co., Inc., and was engineered by a group of scientists from the Public Health Agency of Canada.

Before that study, Merck's vaccine posted 100% efficacy in a novel "ring study" that didn't incorporate a placebo arm.

For the phase 2 study, 500 participants received GSK's shot, 500 received Merck's vaccine and 500 got a placebo.

After initially setting out to test two vaccines on 28,000 volunteers during West Africa's deadly Ebola epidemic, a U.S. -Liberia research team had to dramatically reduce its aspirations when the outbreak started coming to an end. At one week, researchers documented "modest" responses that ended up growing significantly by the one-month point, according to a new release. However, by one month, 71 percent of cAd3-EBOZ recipients and 84 percent of rVSV-ZEBOV recipients developed an antibody response compared to 3 percent of placebo recipients.

After one year, 80 percent of rVSV-ZEBOV recipients and 64 percent of cAd3-EBOZ recipients had antibody responses compared to just 7 percent of placebo recipients.

Some participants who received the test vaccines had temporary mild to moderate side effects, including headaches, muscle pain, fever and fatigue. Overall, no major safety concerns related to the vaccines were identified. Most of the serious medical issues reported during the trial were due to malaria.

Interestingly, at the beginning of the trial investigators found that 4 percent of participants already had a certain threshold of Ebola antibodies - indicative of past Ebola infection - but no known history of Ebola virus disease.

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