Merck's Ebola vaccine is 100% successful in interim Phase III results

Ebolavirus under an electron microscope--Courtesy of CDC

Merck's ($MRK) Ebola vaccine, in development alongside NewLink Genetics ($NLNK), protected 100% of patients from contracting the virus in interim results from an ongoing study, giving rise to hopes it can help prevent future outbreaks.

The vaccine, rVSV-ZEBOV, is in the midst of a big Phase III trial in West Africa, home to the most recent--and deadliest--outbreak of Ebola. In an interim analysis published in The Lancet, every patient who received the vaccine after Ebola broke out in his or her village was virus-free within 6 to 10 days, Merck said, suggesting rVSV-ZEBOV could be a highly effective option for stemming the spread of Ebola.

In a novel trial design, rVSV-ZEBOV's investigators decided against a traditional placebo-controlled trial in favor of a so-called ring study. The researchers identified 7,651 people in Guinea at risk for infection and split them into two groups: Roughly half would receive rVSV-ZEBOV immediately after exposure to Ebola and the rest would get the vaccine after a delay. In the interim analysis, the immediate group reported no infections after 10 days compared with 16 cases of Ebola in the other arm, a highly statistically significant result for rVSV-ZEBOV.

The study, sponsored by the World Health Organization and a slew of global entities, is still ongoing, but the randomization period is over and all patients will from here on out get immediate doses of the vaccine. The investigators are also still assessing its safety, noting that there have been just 43 adverse events in the Phase III study so far.

The vaccine's clinical success suggests it "may be the silver bullet against Ebola," Norway Foreign Minister Børge Brende told The Guardian, "helping to bring the current outbreak to zero and to control future outbreaks of this kind."

The latest Ebola outbreak resulted in nearly 30,000 cases in West Africa over the past year, leading to more than 11,000 reported deaths. And while rates of infection have tailed off over the past few months, rVSV-ZEBOV's developers are hopeful their vaccine could be key to heading off the next outbreak, or at least curtailing its severity.

Merck bought into NewLink's program in November, when the outbreak was at its height, and agreed to handle development, production and commercialization. GlaxoSmithKline ($GSK) and Johnson & Johnson ($JNJ) are at work on Ebola vaccine candidates of their own in concert with global health organizations.

- read the Lancet study (PDF)
- here's Merck's release
- check out the Guardian story