An experimental Ebola vaccine tested on humans has been shown to be 100% effective in final tests. The World Health Organisation led the study of the vaccine after it acknowledged shortcomings in its response to the West Africa outbreak that killed 11,300 people since 2013. The vaccine was developed by the Public Health Agency of Canada and the United States Army and is now licensed to the US-based Merck & Co.

The vaccine, known as rVSV-ZEBOV, is not approved by any regulatory authority yet, but an emergency stockpile of 300,000 doses has been created should an outbreak occur again.

"While these compelling results come too late for those who lost their lives during West Africa's Ebola epidemic, they show that when the next outbreak hits, we will not be defenseless," said Dr. Marie-Paule Kieny, the World Health Organisation's assistant director-general for health systems and innovation and the study's lead author.

"The world can't afford the confusion and human disaster that came with the last epidemic."

A faster way to corner and destroy Ebola

The genetic make-up of the vaccine is a vesicular stomatitis virus (VSV), which sickens cattle but does not infect humans. The gene coding for an Ebola virus surface protein is spliced into the VSV, triggering the immune system to produce antibodies.

"I really believe that now we have a tool which would allow (us) to control a new outbreak of Ebola of the Zaire strain," said Dr. Kieny. "It's the first vaccine for which efficacy has been shown."

The vaccine creates a new, faster, more efficient method to trap and kill the virus. Many small Ebola outbreaks that occurred between 1976 and 2014 were curbed in remote villages by more laborious methods: medical teams flew in, isolated the sick, and wore protective gear to treat them and bury the dead.

However the tactic failed in 2014 when the virus reached more densely populated capital cities, where it spread quickly and dead bodies piled up in the streets.

Vaccine 100% effective but has flaws

The new study confirms what were previous interim results released last year. The results were so outstanding that the study was stopped midway so that everyone exposed to Ebola in Guinea could be immunised.

Last year, 5,837 people were vaccinated with the new vaccine in Guinea, as the virus was waning and all were in contact with a new Ebola patient. They were vaccinated immediately or after three weeks and after a 10-day waiting period, no Ebola cases developed in those immediately vaccinated and only 23 cases out of thousands who got the delayed vaccination after three weeks were infected.

The 10-day window existed due to the "ring vaccination" technique. Upon the discovery of a confirmed case, researchers would contact everyone in contact with the victim. Approximately half the "circles" were offered vaccine and no one who fell ill within the first nine days after vaccination were taken into account as it was assumed that they were infected before the vaccination.

However, experts say it only works against one of the two most common strains of the Ebola virus, and it may not give long-lasting protection. Side effects such as joint pain and headaches were also reported. It is also not known how well the vaccine might work in children since this was not tested in the trial.

"It's certainly good news with regard to any new outbreak - and one will occur somewhere," said Dr. Anthony S. Fauci, director of the National Institute for Allergy and Infectious Diseases, which develops many vaccines and carried out early testing on this Ebola vaccine. "But we still need to continue working on Ebola vaccines."

Other Ebola vaccines are undergoing testing and a vaccine is still needed to protect against another strain, Sudan.

The virus first surfaced in Africa in 1976, causing periodic outbreaks mostly in central Africa, but not as deadly as the West Africa outbreak. Many previous vaccine attempts have failed, partially due to the sporadic nature of outbreaks and shortage of funding. MIMS

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Sources:
https://www.statnews.com/2016/12/22/ebola-vaccine-results/
http://www.bbc.com/news/world-africa-38414060
http://www.nytimes.com/2016/12/22/health/ebola-vaccine.html?rref=collection%2Fsectioncollection%2Fhealth&_r=1