Scientists have a developed a new vaccine that can provide long-lasting immunity against Ebola virus and could potentially be used to reduce infection from the virus among wild African ape populations.
As well as protecting great apes, the study, published in Vaccine, also has implications for future human vaccination against Ebola virus.
"Given the impact of Ebola virus on African ape numbers in the wild, and the role of apes as a route of Ebola virus transmission to humans via the bush meat trade, such a vaccine would be a win-win for humans and wild apes alike," says corresponding author Dr. Michael Jarvis.
African apes are one of the main sources of Ebola virus transmission to humans. Preventing infection among ape populations could reduce the likelihood of future outbreaks among humans. Additionally, Ebola virus is regarded as a major threat to wild ape survival and a successful vaccine could help stabilize endangered populations.
In the multi-institutional study, researchers developed a vaccine based on the cytomegalovirus (CMV) - a common virus capable of infecting almost anyone, that rarely causes symptoms. CMV is typically only a concern for pregnant people or people with weakened immune systems.
The benefits of basing a vaccine on CMV are that it is effective in provoking an immune response, is species-specific and can also spread easily from individual to individual.
One of the biggest hurdles for achieving high vaccine coverage among wild African apes is that many of them live in remote and inaccessible regions, making conventional vaccination almost impossible. A CMV-based Ebola virus vaccine could spread through wild ape populations, conferring high levels of immunity without the need for direct contact.
"We must walk before we can run, but this study provided a little skip," says Dr. Jarvis. "However, this disseminating approach does potentially provide a workable solution to a currently intractable problem of achieving high vaccine coverage in inaccessible ape populations."
Immunity provided by the vaccine protected against Ebola virus for at least 119 days
The work of the researchers is based on an earlier study conducted in 2011, in which they demonstrated the capacity for a CMV-based vaccine to provide protection from Ebola virus in a mouse challenge model.
Like the majority of mouse studies involving Ebola virus, the 2011 study only assessed protection from Ebola virus in the short-term following vaccination. The time period observed is typically 6 weeks after a vaccine is administered.
For the present study, the researchers assessed immunity against Ebola virus for a much longer period. The team demonstrated that the CMV-based vaccine provided long-term immunity, with Ebola virus-specific responses maintained for over 14 months following just one dose. Immunity provided by the vaccine lasted for approximately 4 months (119 days).
The next step for the researchers will be to trial the vaccine in the macaque Ebola virus challenge model, considered to be the "gold standard" in testing vaccines in a model comparable to virus transmission among great apes and humans.
Questions remain that will need answering before a vaccine can be developed for direct use in humans. The researchers have to examine what level of immunity is conferred by disseminated CMV-based vaccines, as up until now the vaccine has only been administered directly.
For now though, the research offers promise. The long-lasting immunity provided by the vaccine in its current form is both crucial to the eventual success of a disseminating vaccine and an attractive characteristic for any vaccine made to be used in humans.
Recently, Medical News Today reported on the story of a doctor from the US who was found to be clear of Ebola virus after receiving an experimental emergency vaccine. The doctor had previously received a needle stick injury while working in an Ebola treatment unit, placing them at high risk of infection.