Authors: Martha Powell, Future Science Group
In a Phase I clinical trial two experimental Ebola vaccine regimens have induced a durable immune response, which persisted for approximately 1 year in healthy volunteers.
The study, published recently in the Journal of the American Medical Association, reported the 1-year data from a single-center, randomized, placebo controlled trial conducted by the Oxford Vaccine Group at the University of Oxford (UK).
The team investigated the immune responses to two investigational vaccines, Ad26.ZEBOV and MVA-BN-Filo, the regimens for which included a heterologous primary vaccine and booster vaccine. Ad26.ZEBOV is an adenovirus type 26 vector vaccine encoding proteins from Zaire ebolavirus, the species responsible for the West African 2014–2015 outbreak. MVA-BN-Filo is also a vector-based vaccine, utilizing a modified vaccinia virus Ankara vector and encoding glycoproteins from various species of Ebola virus and the related Marburg virus.
The trial included healthy adults aged 18–50 years, who were randomized to receive either a placebo or an active vaccine. Of the 75 individuals who received the active vaccine, 64 attended follow-up at day 360 and the team discovered that all of these participants maintained Ebola virus-specific immunoglobulin G. In addition, no serious adverse effects were observed between the previous follow-up, at day 240, and the 1-year follow-up at day 360. The authors stated that to their knowledge this is the longest follow-up duration for any Ebola vaccine schedule with heterologous primary and booster vaccines.
The team write: “Immunity after heterologous primary and booster vaccination with Ad26.ZEBOV and MVA-BN-Filo persisted at 1 year. Although no correlate of protection has yet been established, Ebola virus glycoprotein-specific antibodies appear to play an important role in immunity.”
“A strategy of pre-emptive use of an AD26.ZEBOV followed by MVA-BN-Filo immunization schedule in at-risk populations (where durability of immune response is likely to be of primary importance) may offer advantages over reactive use of single-dose vaccine regimens.”
Although the study demonstrates a promising durability in the immune response triggered by these two experimental vaccines, it does have limitations. The researchers note the study was carried out on a European cohort, suggesting that immune responses may differ in a sub-Saharan African population and presenting the need for the vaccines to also be assessed in this region.
Finally, although the findings so far are promising, further research is necessary to assess the durability of immunity after the 1 year period and also to investigate the immune response to booster doses of vaccine.
Source: Winslow RL, Milligan ID, Voysey M et al. Immune Responses to Novel Adenovirus Type 26 and Modified Vaccinia Virus Ankara–Vectored Ebola Vaccines at 1 Year. JAMA. 317(10) (2017); www.niaid.nih.gov/news-events/experimental-ebola-vaccine-regimen-induced-durable-immune-response-study-finds