Merck & Co. and NewLink Genetics said today that a single dose of their Ebola vaccine candidate rVSV-ZEBOV showed 100% efficacy in an analysis of interim data from a Phase III ring vaccination trial in Guinea.

That analysis and preliminary conclusions from the ongoing study were published today in The Lancet. According to those findings, all individuals who received the vaccine were protected against Ebola virus infection within 6 to 10 days of vaccination.

“The results of this interim analysis indicate that rVSV-ZEBOV might be highly efficacious and safe in preventing Ebola virus disease, and is most likely effective at the population level when delivered during an Ebola virus disease outbreak via a ring vaccination strategy,” the study team concluded.

Between April 1, 2015, and July 20, 2015, 4,123 people were randomly assigned to immediate vaccination with rVSV-ZEBOV, while 3,528 people were randomly assigned to delayed vaccination during the trial, named “Ebola ça suffit,” French for “Ebola, that’s enough.”

“In the immediate vaccination group, there were no cases of Ebola virus disease with symptom onset at least 10 days after randomization, whereas in the delayed vaccination group there were 16 cases of Ebola virus disease from seven clusters, showing a vaccine efficacy of 100%,” the researchers added.

The international team carrying out the trial included researchers from the World Health Organization, the Norwegian Institute of Public Health, the Health Ministry of Guinea, and Médecins sans Frontières.

“The extraordinary efforts of the team in Guinea and other experts have yielded interim results that suggest a potential role for our rVSV-ZEBOV vaccine in the fight against Ebola disease,” Roger M. Perlmutter, M.D., Ph.D., president of Merck Research Laboratories, said a statement.

Added Charles J. Link Jr., M.D., NewLink Genetics’ chairman, CEO, and CSO: “We hope that the interim data published today contribute to the successful registration of our vaccine candidate, which we believe can play an important part in diminishing the threat of Ebola.”

The Guinea trial is one of three ongoing studies in which rVSV-ZEBOV is being evaluated. The other two are:

  • The Sierra Leone Trial to Introduce a Vaccine against Ebola (STRIVE) Phase III study being conducted by the Sierra Leone College of Medicine and Allied Health Sciences, Sierra Leone Ministry of Health, and Sanitation and the U.S. Centers for Disease Control and Prevention (CDC);
  • The Partnership for Research on Ebola Vaccines in Liberia (PREVAIL) Phase II study being conducted by a Liberia-NIH partnership in Liberia.

To date, the rVSV-ZEBOV vaccine has been administered to more than 9,000 people in Phase I, II, and III clinical trials. Vaccinated individuals have been shown to develop antibodies against the Ebola virus, but the significance and durability of this immune response have not been determined.

rVSV-ZEBOV was initially engineered with support from the Public Health Agency of Canada and licensed to NewLink Genetics. To produce the vaccine, the vesicular stomatitis virus was weakened by removing a gene and replacing it with a single Ebola virus gene that alone cannot cause the disease.

In November 2014, during the West Africa outbreak of Ebola, Merck licensed exclusive rights to rVSV-ZEBOV from NewLink Genetics. In February, NewLink Genetics said it received $20 million from Merck for achieving a key clinical development milestone.

In addition to the milestone payment, Merck also agreed to pay NewLink $30 million upfront, according to a NewLink regulatory filing. NewLink also said it was eligible for tiered royalties on sales of the vaccine “in certain markets, subject to certain conditions.”

Joining Merck, NewLink Genetics, and the Public Health Agency of Canada in helping conduct the studies have been NIH and its National Institute of Allergy and Infectious Diseases, the Walter Reed Army Institute of Research, the Canadian Immunization Research Network, and the U.S. Army Medical Research Institute of Infectious Diseases.

Major funding for these studies has come from sources that include the U.S. Department of Defense’s Defense Threat Reduction Agency and Joint Vaccine Acquisition Program, the U.S. Department of Health and Human Service’s Biomedical Advanced Research Development Authority, and the Wellcome Trust.

NewLink Genetics released interim results on rVSV-ZEBOV the same day it disclosed its latest quarterly results. The company finished the second quarter with a net loss of $14.1 million, or ($0.49) per diluted share, compared to a net loss of $9.2 million or ($0.33) per diluted share for Q2 2014.

The company said its R&D expense more than doubled in the second quarter, to $16.1 million, compared with $6.5 million in the year-ago quarter, due to “expenses for manufacturing and research related to the Ebola vaccine candidate,” but primarily due to clinical trial expenses related to its pipeline of product candidates, including its HyperAcute® immunotherapy cancer programs and its IDO pathway inhibitor (indoximod) programs.

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