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Merck & Co.’s vaccine for Ebola is “highly effective,” according to an interim analysis from a panel of experts who recommended that a late-stage trial should continue.

The vaccine was 100 percent effective when it was tested on more than 4,000 people who were in close contact with Ebola patients in the African nation of Guinea, according to a study published today in the Lancet medical journal. The trial of the vaccine, called Ebola ca Suffit -- “Ebola, that’s enough” in French -- began on March 23.

Ebola has killed more than 11,000 people in West Africa following an outbreak that began in late 2013. While the incidence has fallen off sharply, it hasn’t been eradicated, with seven confirmed cases in the week of July 29. The vaccine from Merck is one of several in clinical trials, with GlaxoSmithKline Plc and Novavax Inc. also developing medicines.

“This is an extremely promising development,” Margaret Chan, director-general of the World Health Organization, said in a statement. “An effective vaccine will be another very important tool for both current and future Ebola outbreaks.”

The vaccine was developed by the Public Health Agency of Canada and licensed to NewLink Genetics Corp. In November, Merck entered in an agreement to research, develop and distribute the vaccine. Charles Link, NewLink’s chief executive officer, said the company doesn’t intend to make any significant profit in Africa or developing countries from the potential Ebola vaccine.

“We are really focused on doing everything we can to contribute and help in any material way that we can for the crisis in Africa,” Link said on a conference call Friday to discuss earnings. The agreement with Merck envisions “significant” royalties coming from other parts of the world in the future, he said.

NewLink shares rose 3.3 percent to $52.86 at 10:48 a.m. in New York, while Merck rose 1 percent to $59.11. Kenilworth, New Jersey-based Merck gets more than 10 percent of its $40 billion in annual revenue from sales of vaccines for illnesses such as human papillomavirus, or HPV, and shingles.

Remarkable Achievement

The Lancet, in an editorial accompanying the study, called the result a “remarkable scientific and logistical achievement.”

In the trial, researchers vaccinated anyone in the close circle of contacts of a newly infected person, targeting those most likely to get the disease after a new case. The Lancet called it the largest-scale trial ever performed in Guinea.

People in the study were protected against the Ebola virus within six to 10 days of vaccination. The late-stage trial is continuing, and other studies are in progress, with the goal of submitting the vaccine for regulatory approval around the world.

To create the vaccine, scientists removed a gene from another virus, vesicular stomatitis, and replaced it with an Ebola virus gene that can’t cause the disease alone. That could let people who get the vaccine develop antibodies against Ebola.

It’s still unclear how significant or long the immune response to the vaccine will be, Merck said.

Economic Devastation

The economic disruption caused by Ebola cost Guinea, Liberia and Sierra Leone more than half a billion dollars in 2014, almost 5 percent of their combined gross domestic product, according to the World Bank.

Ebola has proven resilient even in as the countries and international health organizations have stepped up their public-health measures to contain the virus. It reappeared in Liberia in late June, a month after the WHO had declared an end to the Ebola’s spread there.

(Updates with NewLink’s comments in sixth paragraph.)