After 15 years of development, Merck’s vaccine has proven to be 100% effeective at preventing Ebola virus in a clinical trial.  However, it will not be a long term solution,

Marie-Pierre Preziosi, head of the Initiative for Vaccine Research at the World Health Organization, which led the clinical trial, said that the vaccine is suppose to be used to stop the spread of an existing outbreak. Only people most at risk of being exposed to a Ebola-infected person like healthcare worker would receive the vaccine if it is approved.

Preziosi also said that the vaccine will not be given as a preventive vaccine on a large scale as there is not enough information to prove how long the vaccine’s protection lasts. If the vaccine is approved by drug regulators, it will not be used as a long term solution to prevent Ebola cases.

Nearly 12,000 people in Guinea were involved in the trial, which began in 2015. Among the  approximate 6,000 people who received the vaccine, no Ebola cases were identified 10 days or more after vaccination. Among those who did not receive the vaccine, 23  Ebola cases surfaced within the same period.

Manufactured by Merck, the vaccine uses a genetically engineered version of vesicular stomatitis virus, an animal virus that primarily affects cattle, to carry an Ebola virus gene insert. The final results of the trial were published at the end of last month in the Lancet.

Despite having impressive study results, there are still many uncertainties about the vaccine, which includes its effectiveness and safety for pregnant women, HIV-positive individuals, and young children.

Studies in HIV-positive individuals and children younger than six are just getting started, says Tom Monath, chief scientific officer and chief operations officer at NewLink Genetics, which initially licensed the vaccine from Canadian government scientists and is collaborating with Merck.

Scientists will be able to obtain limited data from these extra studies. Since the Ebola outbreak has ended, researchers will not be able to measure the vaccine’s efficacy in these subjects. They also can’t expose trial volunteers to Ebola since the virus is fatal.

Preziosi said that a mixture of Ebola therapeutics and vaccines, including those that are able to  protect against different strains of the disease, will be required to effectively thwart and respond to future epidemics. (Mullin, 2017)

Source: Mullin, E. (2017). Merck’s Vaccine Won’t Be the End of Ebola. Retrieved from


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