The vaccine, called rVSV-ZEBOV, does not contain any live Ebola virus. Instead it replaces a gene that encodes an Ebola virus surface protein with a gene from a harmless virus known as vesicular stomatitis virus.
The biggest recent trials with the vaccine took place in a coastal region of Guinea at the tail end of a major outbreak in 2015. The trial involved 5,837 people receiving the vaccination using an innovative delivery strategy called 'ring vaccination'.
The approach involves a research team tracing clusters of people related to each new diagnosed case. Every time a new Ebola diagnosis is made vaccinations are delivered to all who may have come into contact with that person over a three week period. In the instance of the Guinea trial there were 117 clusters identified, with each "ring" of people consisting of around 80 individuals. The experiment was extraordinarily successful with not one person who recieved the vaccination contracting the virus. The strategy also seemed to offer a strong degree of herd immunity to those close to the clusters but not themselves vaccinated.
This will be the first time the vaccine has been deployed with the goal of stopping an outbreak before it can spread. The first batch of 4,000 doses recently arrived in the country from a World Health Organization (WHO) stockpile in Geneva. Merck, the pharma company that owns the vaccine, has a further 300,000 doses in the United States that were stockpiled as part of an arrangement with the WHO for emergency uses.
The vaccines are currently housed in the country's capital Kinshasa before hopefully being transported and deployed to the outbreak hotspot of Bikoro within days. The transportation of the vaccine is slowed by the need for it to be stored at extreme, subzero temperatures. This means a cold-chain must be established to move the vaccine around. The town of Bikoro is notoriously difficult to reach, making movement of the vaccine challenging.
"This is not a simple logistical effort; it's not like doing a polio campaign with oral polio vaccines, where we get it immediately out to the field," explained Peter Salama from the WHO. "This is a highly complex sophisticated operation in one of the most difficult terrains on Earth."
The deployment of this experimental vaccine will prove a major test for not only the efficacy of the vaccine but for global health strategies designed to respond to major viral outbreaks such as this. And despite the frightening threat of this devastating virus spreading to one of the country's larger cities, at least health workers now have a new weapon in their arsenal.
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