Ebola Resource Center
Ebola Resource Center
December 28, 2016
2 min read

Ebola vaccine 100% effective in major trial

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An experimental Ebola virus vaccine was 100% effective at preventing the disease during a ring vaccination trial conducted in Guinea where the deadly West African outbreak began 3 years ago.

Researchers said findings from the “Ebola Ça Suffit!” (“Ebola That’s Enough!”) trial in Guinea backed up interim results published last year showing the effectiveness of rVSV-ZEBOV — a recombinant, vesicular stomatitis virus-based vaccine candidate developed by the Public Health Agency of Canada.

Marie-Paule Kieny
Marie-Paule Kieny

“While these compelling results come too late for those who lost their lives during West Africa’s Ebola epidemic, they show that when the next Ebola outbreak hits, we will not be defenseless,” Marie-Paule Kieny, PhD, WHO’s assistant director-general for health systems and innovation, said in a statement.

The largest Ebola outbreak on record began in Guinea in December 2013 and infected more than 28,000 people — mostly in Guinea, Liberia and Sierra Leone — but may have been even larger. It killed more than 11,300 people, including one in the United States.

Although it has been almost a year since WHO declared the end of transmission in West Africa, some flare-ups largely related to virus persistence in Ebola survivors have occurred, including in Guinea.

In 2015, Kieny and colleagues identified 11,841 people in 117 clusters in the Guinea’s coastal Basse-Guinée region who were either contacts or contacts of contacts of patients with confirmed Ebola virus infection. The researchers vaccinated 5,837 of them, randomly assigning clusters to receive either immediate vaccination or delayed vaccination 21 days after randomization.

No cases of Ebola virus disease occurred in any of the contacts who were immediately vaccinated. Further, vaccination protected both vaccinated and unvaccinated people in those clusters, Kieny and colleagues said.

In comparison, 23 cases occurred in contacts who received either a delayed vaccination or no vaccination at all.

The results were published in The Lancet.

“Ebola left a devastating legacy in our country. We are proud that we have been able to contribute to developing a vaccine that will prevent other nations from enduring what we endured,” KeÏta Sakoba, MD, coordinator of the Ebola response and director of the National Agency for Health Security in Guinea, said in a statement.

According to Kieny and colleagues, just two serious adverse events were related to vaccination — one febrile reaction and one anaphylaxis — while one influenza-like illness was possibly related. All three recovered without sequalae, they said.

In a related editorial, Thomas W. Geisbert, PhD, professor of microbiology and immunology in the University of Texas Medical Branch, said previous safety concerns about rVSV-ZEBOV may have been alleviated but questions remain about how durable the vaccine is.

However, Geisbert also noted the strength of the results showing that rVSV-ZEBOV was effective at preventing infection.

“After 40 years,” he wrote, “we appear to now have an effective vaccine for Ebola virus disease to build upon.” – by Gerard Gallagher.


Geisbert TW. Lancet. 2016;doi:10.1016/S0140-6736(16)32618-6.

Henao-Restrepo AM, et al. Lancet. 2016;doi:10.1016/S0140-6736(16)32621-6.

Disclosures: The vaccine is licensed to NewLink Genetics and Merck. Please see the full study for a list of all authors’ relevant financial disclosures. Geisbert reports having five U.S. patents and two provisional U.S. patents, including some related to Ebola virus vaccines.