Final trial results confirm Ebola vaccine provides high protection against disease

Initially, rings were randomised to receive the vaccine either immediately or after a 3-week delay, and only adults over 18 years were offered the vaccine. After interim results were published showing the vaccine’s efficacy, all rings were offered the vaccine immediately and the trial was also opened to children older than six years.

In addition to showing high efficacy among those vaccinated, the trial also shows that unvaccinated people in the rings were indirectly protected from Ebola virus through the ring vaccination approach (so-called “herd immunity”). However, the authors note that the trial was not designed to measure this effect, so more research will be needed. 

“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” said Dr. KeÏta Sakoba, Coordinator of the Ebola Response and Director of the National Agency for Health Security in Guinea.

To assess safety, people who received the vaccine were observed for 30 minutes after vaccination, and at repeated home visits up to 12 weeks later. Approximately half reported mild symptoms soon after vaccination, including headache, fatigue and muscle pain but recovered within days without long-term effects. Two serious adverse events were judged to be related to vaccination (a febrile reaction and one anaphylaxis) and one was judged to be possibly related (influenza-like illness). All three recovered without any long term effects.

It was not possible to collect biological samples from people who received the vaccine in order to analyse their immune response. Other studies are looking at the immune response to the vaccine including one conducted in parallel to the ring trial among frontline Ebola workers in Guinea.

“This both historical and innovative trial was made possible thanks to exemplary international collaboration and coordination, the contribution of many experts worldwide, and strong local involvement,” said Dr John-Arne Røttingen, specialist director at the Norwegian Institute of Public Health, and the chairman of the study steering group.

In January, GAVI, the Vaccine Alliance provided $5 million to Merck towards the future procurement of the vaccine once it is approved, prequalified and recommended by WHO. As part of this agreement, Merck committed to ensure that 300,000 doses of the vaccine are available for emergency use in the interim, and to submit the vaccine for licensure by the end of 2017. Merck has also submitted the vaccine to WHO’s Emergency Use and Assessment Listing procedure, a mechanism through which experimental vaccines, medicines and diagnostics can be made available for use prior to formal licensure.

Additional studies are ongoing to provide more data on the safety of the vaccine in children and other vulnerable populations such as people with HIV. In case of Ebola flare-ups prior to approval, access to the vaccine is being made available through a procedure called “compassionate use” that enables use of the vaccine after informed consent. Merck and WHO’s partners are working to compile data to support license applications.

The rapid development of rVSV-EBOV contributed to the development of WHO’s R&D Blueprint, a global strategy to fast-track the development of effective tests, vaccines and medicines during epidemics.

Also published in The Lance , is a phase 2 trial of a different Ebola vaccine candidate, the recombinant adenovirus type-5 Ebola vaccine. The trial was led by the Beijing Institute of Biotechnology and was conducted in Sierra Leone in 2015. It involved 500 healthy participants, followed for 6 months – 250 were given a high dose vaccine, 125 a low-dose and 125 a placebo. The study found that the vaccine was safe and induced an immune response that peaked at 28 days, but decreased during the six months post injection. One serious adverse event was reported, in an individual with a history of asthma. Further research on this vaccine is needed in order to assess its efficacy.

— Read more in Feng-Cai Zhu et al., “Safety and immunogenicity of a recombinant adenovirus type-5 vector-based Ebola vaccine in healthy adults in Sierra Leone: a single-centree randomised, double-blind, placebo-controlled, phase 2 trial,” The Lancet (22 December 2016) (DOI: 10.1016/S0140-6736(16)32617-4)