A preclinical study testing the efficacy of the Ebola vaccine VSV-EBOV against the newly emerged West African Ebola strain shows complete protection when administered seven days before infection in nonhuman primates, and partial protection when administered three days before infection.
The positive results of this study further reveal the mechanisms by which an effective immune response is mounted against the Ebola virus, aspects of which have been unclear.
In the study by Andrea Marzi et al., VSV-EBOV was administered to groups of macaques 28, 21, 14, 7, or 3 days before infection with the Makona strain of Ebola. No adverse effects were detectable after immunization with the lethal dose, and the animals were then monitored for 42 days.
The control group, which was administered a vaccine known not to be effective, showed severe symptoms of Ebola and did not survive. One animal in the day-3 VSV-EBOV vaccination group also did not survive, while the other two animals in this group presented mild and moderate symptoms of Ebola but eventually cleared the virus.
All nine remaining animals in the day-28, -21, -14, and -7 vaccination groups did not develop any clinical signs of disease. The presence of immunoglobulin G (IgG) antibodies for Ebola has been associated with survival in previous studies; at the time of infection, animals in the day-28, -21 and -14 vaccination groups showed high levels of these Ebola-specific antibodies.
Although, day-3 and -7 groups did not have Ebola-specific antibodies at the time of infection, day-3 immunized animals had measurable Ebola-specific IgG antibodies six days after being infected with Ebola, offering them partial protection.
The researchers suggest that the VSV-EBOV vaccine provokes a strong innate immune response that helps limit virus replication during the critical period as the body develops Ebola-specific antibodies. This work shows the potential of this vaccine for rapid deployment to contain any future outbreaks.
Read more: VSV-EBOV rapidly protects macaques against infection with the 2014/15 Ebola virus outbreak strain.
