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Ebola vaccine completely effective, say researchers

Merck earns plaudits for ‘game-changing’ vaccine

WHO Ebola workers 

 Ebola outbreak in West Africa (WHO | Stephane Saporito)

An Ebola vaccine fast-tracked through clinical development has shown 100% efficacy in a phase III trial after a single dose, surpassing all expectations.

The rVSV-ZEBOV candidate developed by Merck & Co and NewLink Genetics seemed to protect subjects who had been in close proximity to an infected Ebola patient from the virus, with immunity kicking in within six to 10 days of vaccination.

While the 4,000-patient trial is continuing, the scientists behind the study in Guinea say the data so far suggest the vaccine "might be highly efficacious and safe in preventing Ebola virus disease."

The team from the World Health Organization (WHO), the Norwegian Institute of Public Health, the Health Ministry of Guinea and Médecins sans Frontières (MSF), amongst others, said the results suggest rVSV-ZEBOV could be used in a "ring" vaccination strategy.

That means it could be given to clusters individuals exposed to an infected patient in order to prevent the virus spreading, a more manageable strategy than broad, population-wide immunisation.

"This trial design is logistically feasible, even in resource-poor settings and in a crisis situation," say the scientists, who have published their findings in The Lancet.

WHO vaccine specialist Marie Paule Kieny - who co-authored the trial report - said the results were a "game-changer" that will have an impact on the management of both the current Ebola outbreak as well as any future outbreaks.

In the trial, patients exposed to an Ebola case were randomly assigned to either immediate vaccination with rVSV-ZEBOV or delayed vaccination 21 days later. The primary outcome measure was laboratory-confirmed Ebola virus disease with onset of symptoms at least 10 days after randomisation.

No patients in the immediate vaccination group became sick, while 16 people from in the delayed arm fell ill. Furthermore, no new Ebola cases were seen in either the immediate or delayed groups from six days post-vaccination.

The companies are taking a cautious stance on the data, stressing it is important that it is subjected to stringent review from all interested parties before drawing any firm conclusions on the role of the vaccine.

The WHO said in a statement that while the vaccine up to now shows 100% efficacy in individuals, "more conclusive evidence is needed on its capacity to protect populations through what is called 'herd immunity'."

"To that end, the Guinean national regulatory authority and ethics review committee have approved continuation of the trial" added the agency, which also noted that the enrolment criteria will be changed to allow recruitment of 13 to 17-year-old and possibly 6 to 12-year-old children, now that there is evidence of its safety.

As of the end of July, there had been a total of 27,748 reported confirmed, probable, and suspected cases of Ebola in Guinea, Liberia and Sierra Leone, with 11 279 reported deaths, according to WHO figures.

Merck bought the rights to NewLink's vaccine in November 2014, and a phase I trial in the US was halted earlier this year after patients reported joint pain after administration.

Other groups developing a potential vaccine for Ebola include Johnson & Johnson, whose two-shot vaccine is currently in phase I trials.

GlaxoSmithKline (GSK) which has its ChAd3-EBO candidate -partnered with the US National Institute for Allergy & Infectious Diseases (NIAID) - in phase II.

Article by
Phil Taylor

3rd August 2015

From: Research



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