The experimental Ebola vaccine trial that immunized 60 volunteers at the University of Oxford’s Jenner Institute indicates that the vaccine is safe, though its potency remains uncertain.
The Ebola vaccine, developed by GlaxoSmithKline and the US National Institutes of Health, has been tested on about 250 healthy volunteers in the US, UK, Switzerland and Mali. Whilst the results of the safety trials at Oxford suggest that the vaccine generates an immune response against Ebola with nil or very mild side effects, the effectiveness of the response has been questioned.
Professor Adrian Hill, the lead researcher of the study, said of the immune responses produced by the GSK/NIH vaccine: “Are they going to be strong enough to actually protect people against Ebola?”
Though preliminary trials on macaque monkeys conducted by the US National Institutes of Health demonstrated that vaccinated monkeys developed long-term immunity to the Ebola virus lasting at least 10 months, human immune responses have been lower and less promising. T-cell generation, a critical aspect of immunogenicity, was several times lower in humans than seen in immunized monkeys.
Professor Sarah Gilbert from the Jenner Institute said: “No one can predict how effective the vaccine will be, but we know that everyone vaccinated with the ChAd3 vaccine makes an immune response to it, and that will give their immune system a head start in dealing with the Ebola virus if they are exposed to it.
“This might result in vaccinated individuals suffering a much milder illness, and a reduction in the fatality rate, and since it is people with severe illness who are most infectious to others, it could also help stop further infections.”
Though the overall potency of the vaccine response remains unclear, scientists remain hopeful and seek to immunize 30,000 volunteers in Liberia at a higher dose concentration in the hope that it will yield a better immune response.
Dr Jeremy Farrar, director of the Wellcome Trust, a co-funder of the trial, said: “This study is very encouraging as it provides good initial evidence that the GSK vaccine will be safe to use in people. However, we still don’t know whether it will provide protection against Ebola infection in a real-world situation. That’s why trials in West Africa of this, and the other vaccines in development, must begin as soon possible.”
Last week, GSK shipped the first batch of the vaccine to Liberia, where a large-scale randomized trial is soon expected to begin. Other prototype vaccines are to be tested in Sierra Leone and Guinea.