“Ebola That’s Enough!” Finally a Vaccine.
An Ebola vaccine might soon be available. A group of scientists and doctors conducted a ring vaccination study of a recombinant Ebolavirus vaccine in Guinea, West Africa. The vaccine referred to as rVSV-ZEBOV is a replication-competent, vesicular stomatitis virus-based candidate vaccine, that expresses surface glycoproteins of the Zaire Ebolavirus. The vaccine was tested for efficacy in the prevention of Ebola Virus Disease, in people at risk, from being exposed to newly confirmed cases of Ebola.
A safe and effective human Ebola vaccine is needed.The Ebola virus was first identified in Africa during 1976, and since then there have been many sporadic deadly outbreaks of the disease. The most recent Ebola outbreak in West Africa started in 2013, and lasted three years. The virus is spread mainly by contact within familial and social networks, and funerals (during the preparation and handling of the infected body). Currently, there is no vaccine available to prevent disease from the Ebola Virus .
Animal studies suggested that the vaccine would be well tolerated in humans. When tested in animal models using rodents and non-human primates, rVSV-ZEBOV was found to be protective. Primates treated with just a single dose of the vaccine were completely protected when exposed to high-levels of Ebolavirus.
A phase 3, ring vaccination trial was undertaken to test safety and efficacy in humans. The novel ring vaccination study was designed to gather evidence of vaccine efficacy and safety, in individuals and groups; where the incidence of a disease is low and decreasing.
Initially conducted in adults who came in contact with the virus, the study was expanded to include children ages 6 to 17 year in 2015. The findings of the trial were consistent with animal studies and a Phase 2 study done in humans, that showed the vaccine to be 94% effective in 500 individuals.
Ebola ça Suffit! (Ebola that’s Enough!)–Phase 3 Ring Vaccination Study
Those who came in contact with confirmed cases of the disease, and those who they were in contact with, were referred to as “contacts” , and “contacts of contacts”. Contacts were defined as individuals who lived with or visited a person confirmed to be infected with Ebola virus, after symptoms developed. Contacts would have provided unprotected care to the infected, or dressed the body for funeral. In addition to these contacts, they would have had contact with the patients body, body fluids, linens, or clothes. Contacts of Contacts were neighbors of the infected patient or household members of primary contacts – who did not live near the infected.
All together, 98 clusters of epidemiologically linked people were identified, and consisted of over five thousand contacts and contacts of contacts. Those eligible for the study were either randomly or non-randomly assigned to immediate vaccination or delayed vaccination. All people who were NOT randomly assigned, received the vaccine immediately. The randomly assigned group, was divided into immediate and delayed vaccination categories.
After ten days from the point of vaccination, subjects were monitored for the development of Ebola Virus Disease. The groups that received delayed vaccination, did so 21 days after being assigned, and had 16 cases of the disease arise. Another 7 cases of the disease developed in those who were identified by the study, but never vaccinated. However, in all contacts who were immediately vaccinated, no cases of the disease were reported, or found.
Even though, only a little more than half of the contacts and contacts of contacts assigned to the immediate vaccination group received the vaccine, none of the people in those groups developed Ebola. The rVSV-ZEBOV vaccine protected both vaccinated and unvaccinated people in the same clusters, demonstrating not only efficacy but also herd immunity. Overall, the vaccine was determined to be 100% effective in preventing Ebola Virus Disease.
After preliminary results of the phase 3 human trial indicated 100% efficacy in the immediate vaccination groups, the delayed-vaccinated portion of the study was cancelled. In a non-human primate study, the vaccine only conferred partial protection to primates vaccinated less than a week before exposure to the virus. Due to a lag period between the time of vaccination and the induction of an immune response, immediate vaccination is necessary for complete protection from the virus.
Ebola Vaccine rVSV-ZEBOV
Developed by Merck, the rVSV-ZEBOV Ebola vaccine is administered intramuscularly, and confers short-term protection through the activation of innate immunity. During this time, the virus is restricted from replicating, and thereby prevented from developing adaptive responses necessary for evading the immune system. rVSV-ZEBOV offers substantial protection against Ebola Virus Disease without risk to safety. Adverse events associated with the vaccine were mild, and consisted mainly of headache, fatigue, and muscle pain. A little over 50% of vaccine recipients reported at least one of these adverse events within 14 days following vaccination. Approximately 1% of recipients reported experiencing a severe adverse event. Of the 80 cases reported, only 2 were determined to be related to the vaccine. One subject had a febrile reaction, while another suffered anaphylaxis. There was one other case, in which the subject developed a flu-like illness, but its relation to the vaccine could neither be confirmed nor denied. All 3 subjects recovered without further complications.
Conclusion: Ring Vaccine Prevention Is Promising
rVSV-ZEBOV is a promising vaccine candidate, as it is safe and effective in the prevention of Ebola Virus Disease. As a weapon in the control of the disease, It may contribute to shortening the magnitude and duration of the epidemic of Ebola Virus Disease in West Africa. Additionally, the ring vaccination method coupled with surveillance and containment strategies could significantly contribute to the containment of future Ebola outbreaks, by identifying and treating all persons who may have had primary or secondary contact with the infected.