New Ebola Vaccine Highly Effective in Preventing Spread of Disease

A new Ebola virus vaccine has been shown to be highly effective in preventing the development of Ebola in people recently exposed to the virus, according to a large-scale, cluster-randomized ring vaccination trial reported recently in the Lancet.¹

The researchers, led by Ana Maria Henao-Restrepo, MD, a scientist with the World Health Organization (WHO), monitored a designated region in Africa for reported cases of Ebola. Using a “ring” approach unique to testing vaccines in community settings where recent outbreaks have occurred, they identified randomized clusters of epidemiologically linked people around the first-reported “index” case of Ebola. The people in the ring cluster were given a single intramuscular dose of a candidate vaccine for Ebola virus, rVSV-ZEBOV, either immediately or 21 days after the identification of the index case.

The clusters of Ebola outbreaks identified by Dr Henao-Restropo and colleagues occurred in a region of Guinea between March of 2015 and January of 2016. A total of 4539 direct contacts and contacts of those contacts in 51 clusters were assigned to immediate vaccination on Day 0, and 4557 individuals in 47 clusters were randomly assigned to delayed vaccination given on Day 21.

Over the first 10 days, the two groups experienced similar rates of Ebola, with 20 patients given immediate vaccination and 21 given delayed vaccination developing the virus. After 10 days, however, no further cases were reported among the cases from the 51 clusters that had received immediate vaccination, while 16 new cases developed in vaccinated people from 11 of the 47 delayed-vaccination clusters. In total, 105 cases of Ebola (among vaccinated and unvaccinated individuals) were reported, which included people in the delayed-vaccination clusters and people who had never been inoculated, for an attack rate of 0.9%.

Altogether, 5837 people consented to be vaccinated in both groups. Immediate vaccination was considered 100% effective in protecting both vaccinated and unvaccinated people in the affected ring clusters, which the investigators attributed to an “interruption effect” on the transmission of the virus within immediately vaccinated clusters.

Adverse effects were generally mild, including headache (25.4%, n = 1832), fatigue (18.9%, n = 1361), and muscle pain (13.1%, n = 942), all reported within 14 days of vaccination. Of 80 serious adverse events reported, only 2 were deemed to be due to the vaccine, and 1 was deemed “possibly” due to the vaccine; all 3 patients recovered.

Dr Henao-Restrepo and colleagues reiterated that none of the people who were immediately vaccinated developed Ebola more than 10 days after vaccination. An accompanying editorial by Geisbart³ pointed out that the durability of this vaccine has yet to be tested, as the study only involved an 84-day follow-up. At this point, Geisbart wrote, “Is it still protective, for example 2 to 3 years after the vaccination?”

Since the identification of the Ebola virus in 1976, it has been associated with extremely high mortality in African countries.³ The high efficacy of the rVSV-ZEBOV offers significant opportunity not only to halt outbreaks among people who are immediately vaccinated, but also to prevent transmission to nonvaccinated individuals in the same community clusters.

References

1. Henao-Restrepo AM, Camacho A, Longini AM, et al. Efficacy and effectiveness of an rVSV-vectored vaccine in preventin Ebola virus disease: final results from the Guinea ring vaccination open-label, cluster randomized trial (Ebola Ça Suffit) [published online December 23, 2016]. The Lancet. doi.org/10.1016/S0140-6736(16)32621-6
2. Griesbart TW. First Ebola virus vaccine to protect human beings? [published online December 22, 2016].  The Lancet.  doi.org/10.1016/S0140-6736(16)32618-6
3. World Health Organization (WHO). Ebola virus disease fact sheet. 2016. www.who.int/mediacentre/factsheets/fs103/en/. Accessed Nov 30, 2016.