- Large randomized,
placebo-controlled, phase 2 clinical trial in Liberia show that two
candidate Ebola vaccines pose no major safety concerns.
- The vaccines elicit immune
responses by one month after initial vaccination that last for at least
- The study
included 1,500 adults and began during the West Africa Ebola outbreak.
time when Ebola virus disease
(EVD) outbreak began in December 2013 in western Africa, there were no
vaccinations available. Research has allowed the development of candidate
vaccines against Ebola in recent years. Two such candidate vaccines have been
put through a placebo-controlled phase 2 clinical trial in Liberia. The study
included 1,500 adults and the results of the large randomized study are
published in the New England Journal of
Overview of the study
study tests the efficacy of two candidate vaccines, chimpanzee adenovirus 3
vaccines, (CAd3-EBOZ) and the recombinant vesicular stomatitis virus vaccine
(rVSV-ZEBOV) and began during the West Africa Ebola outbreak. The trial is
being conducted by a U.S.-Liberia clinical research collaboration known as the Partnership
for Research on Ebola Virus in Liberia (PREVAIL)
, established in 2014 in
response to the request from the Liberian Minister of Health to the U.S.
Secretary of Health and Human Services. The trial is sponsored by the National
Institute of Allergy and Infectious Diseases (NIAID).
‘The candidate vaccines had no major safety concerns and elicit an immune response by one month after initial vaccination that lasts for at least one year.’
study included a total of 1,500 participants including men and women above the
age of 18 with no reported history of Ebola virus disease. The participants
were divided into three groups with 500 people in each and were followed for 12
months. The volunteers received one of the vaccine candidates or a placebo
(saline injection). Participants were asked to provide blood samples before
vaccination and again at one week, one month, six months and one year
post-vaccination. Investigators then tested each of these samples for
antibodies to the Ebola virus.
- One month response: 71 percent
of cAd3-EBOZ recipients and 84 percent of rVSV-ZEBOV recipients developed
an antibody response compared to 3 percent of placebo recipients.
- One year response: 64 percent of
cAd3-EBOZ recipients and 80 percent of rVSV-ZEBOV recipients had an
antibody response compared to 7 percent of placebo recipients.
- Adverse side effects: 20
participants had a serious adverse event, including 6 CAd3-EBOZ
recipients, 6 in rVSV-ZEBOV recipients and 8 in the placebo group.
- However, a total of 70% of the
serious adverse events in the first 30 days after injection were
attributed to malaria.
- Overall, investigators did not
identify any major safety concerns related to the vaccines.
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 NIAID Director Anthony S. Fauci, M.D.
"A safe and effective vaccine would be a critically important addition to
classical public health measures in controlling inevitable future Ebola
- Kennedy SB, Bolay F, Kieh M, et al. Phase 2 placebo-controlled trial of two vaccines to prevent Ebola in Liberia. N Engl J Med 2017;377:1438-1447