An experimental vaccine, ChAd3, to prevent Ebola virus disease has been found to be well-tolerated and produced immune system responses in all 20 healthy adults who received it in a Phase 1 clinical trial, US researchers said. Mzapp is another vaccine under trials.
The trials were conducted at US National Institutes of Health’s clinical centre in Bethesda, Maryland after they were successfully experimented on animals in September. The ChAd3 vaccine has been co-developed by the NIH’s National Institute of Allergy and Infectious Diseases (NIAID) and GlaxoSmithKline (GSK).
“Based on these positive results from the first human trial of this candidate vaccine, we are continuing our accelerated plan for larger trials to determine if the vaccine is efficacious in preventing Ebola infection,” said NIAID director Anthony S. Fauci.
The Ebola vaccine ChAd3 contains antigenic material from both the Zaire and Sudan strains of Ebola and the safety results have been out now after two months of trial on humans. The Ebola virus genetic material is delivered by a carrier virus derived from chimpanzees that causes a common cold in chimpanzees but causes no illness in humans, the researchers said.
Since the candidate vaccine does not contain Ebola virus, it cannot cause Ebola virus disease, they said. During their clinical trial, the researchers in maryland enrolled volunteers between ages 18 and 50. in all 20 volunteers habe participated in the trial. Ten volunteers received vaccine at a lower dose and 10 others received the same vaccine at a higher dose to arrive at comparative results.
The results were monitored at two weeks and four weeks following vaccination, and the researchers tested the volunteers’ blood to determine if anti-Ebola antibodies were generated. The results were positive.
All 20 volunteers developed such antibodies within four weeks of receiving the vaccine and antibody levels were higher in those who received the higher dose vaccine. The researchers also analyzed whether the vaccine prompted production of immune system cells called T-cells.
The experimental vaccine did induce a T-cell response in many of the volunteers including production of CD8 T cells which may be an important part of immune protection against Ebola viruses, according to the researchers.
Four weeks after vaccination, CD8 T cells were detected in two volunteers who had received the lower dose vaccine and in seven of those who had received the higher dose, making it viable that higher dosage will help quickly develop antibodies but even smaller dosage does but in a delayed phase.
“The size and quality of the CD8 T cell response we saw in this trial are similar to that observed in non-human primates vaccinated with the candidate vaccine,” noted the trial’s principal investigator Julie E. Ledgerwood.
Since the initial tests showed these vaccines are safe, and able to make the immune system respond, the trial will be expanded to African countries – possibly as soon as January 2015.
There are several other molecules in development for potential Ebola vaccines. The NIH and Thomas Jefferson University are developing an Ebola vaccine based on a rabies vaccine. It will be a trivalent vaccine, containing antigenic material from Zaire and Sudan strains of Ebola virus as well as the Marburg virus. Animal studies are being conducted and human safety studies will be taken up next year in January.