A consortium of researchers has reported that an Ebola vaccine appears to provide volunteers protection against the virus two years after they were injected.
The new study, published in the Lancet Infectious Diseases showed that the volunteers had high and stable levels of antibodies to the Ebola Zaire virus, two years after immunisation.
Volunteers who received a high dose of the vaccine had, on average, higher antibody levels than people who received a lower dose. But there were solid levels of antibodies even among those who got the lower dose.
“The ideal vaccine in these regions would have long-term durability,” said lead author Dr Angela Huttner, an infectious diseases specialist at Switzerland’s University Hospitals of Geneva. The vaccine is meant to provide protection in regions with logistical challenges, where getting booster shots would be impractical.
A fast-acting, long-lasting vaccine given in a single dose would be an effective tool for controlling dangerous Ebola outbreaks. Vaccinating healthcare workers, for instance, could prevent the type of spread within hospitals that, in the early days of an outbreak, can turn a smouldering outbreak into a conflagration.
For this study, researchers pooled data with two other groups that conducted Phase 1 trials of the vaccine in Africa — in Lambaréné, Gabon, and Kilifi, Kenya. In total, they had data from 197 people who received the vaccine.
Both the Geneva and the Gabon volunteers will be followed for five years to see what happens to antibody levels over time. The Kenyan trial, however, ended.
The study tracked two years of antibody levels for the people vaccinated in Geneva and one year each in Gabon and Kenya. It found that antibodies that specifically target the main protein on the exterior of the Ebola virus remained high.
But levels of neutralising antibodies dropped quite quickly. Huttner noted, however, that this may be a testing problem, because there isn’t a good test to measure neutralising antibodies for Ebola.
The researchers are hopeful that the data will prove to be predictive of long-term protection, in five years.
Blood samples from Geneva volunteers at the three-year mark have already been collected, though they are yet to be analysed for antibody levels.
An earlier study conducted in Guinea showed the vaccine from Merck, which is given in a single shot, rapidly generated protection against the virus.
But how long that protection lasts remained an open question. Merck is working towards a 2018 licensure filing with the Food and Drug Administration of the US.
If approved, the vaccine could help in healthcare emergency response settings following an outbreak and to protect scientists who work with the Ebola virus.