An Ebola survivor sits in her bedroom in Beni, north eastern Democratic Republic of the Congo on Sept. 17.

Sign up to our Next Africa newsletter and follow Bloomberg Africa on Twitter

U.S. regulators have approved a vaccine to protect against the deadly Ebola virus, a crucial step in the battle against an infection that’s considered one of the world’s deadliest killers.

The vaccine, developed and made by Kenilworth, New Jersey-based Merck & Co., was found to be 100% effective when given at least 10 days in advance of potential exposure, the U.S. Food and Drug Administration said. The tests were conducted in Guinea, during a 2014 to 2016 outbreak.

“The FDA’s approval of Ervebo is a major advance in helping to protect against the Zaire ebolavirus as well as advancing U.S. government preparedness efforts,” said Peter Marks, director of the FDA’s Center for Biologics Evaluation and Research, in a statement.

The vaccine is given as a single injection and appears to be most effective when patients have time to build immunity before being exposed to the virus. It’s not clear how long protection from the shot lasts. The effectiveness of some inoculations can fade over time.

Drugmaker Johnson & Johnson has a second vaccine in development, though earlier this year public health authorities had made the Merck shot their focus for deployment in the outbreak. An ongoing outbreak in the Democratic Republic of Congo has killed more than 2,000 people, according to the World Health Organization.

In the U.S., Ebola has typically been brought back by patients infected elsewhere who have in some rare circumstances infected the nurses and doctors caring for them. But the approval by the FDA marks a milestone in the fight against a terrifying virus that has killed thousands in parts of Africa, and has worried health and government leaders in developed nations as well.

“While the risk of Ebola virus disease in the U.S. remains low, the U.S. government remains deeply committed to fighting devastating Ebola outbreaks in Africa, including the current outbreak in the Democratic Republic of the Congo,” said Anna Abram, FDA Deputy Commissioner for Policy, Legislation, and International Affairs.

Deployment

Vaccines can be deployed to inoculate health workers, or to build a wall of immunity in the communities facing or near an outbreak. Viruses depend on their hosts to spread, and vaccines -- whether for the flu, polio or other diseases -- have been crucial tools in stopping some of the world’s most dire illnesses.

Merck said in a statement that it was working on ramping up production of the vaccine to be available in the third quarter of 2020. In the meantime, it will continue providing a version of the shot that was used in the trial.

The company hasn’t established a price for the drug. The drugmaker is working with Gavi, a nonprofit that provides support to global vaccine programs. The organization works throughout much of sub-Saharan Africa.

“Merck has committed to making the vaccine available to Gavi-eligible countries at the lowest possible access price,” Merck spokeswoman Pam Eisele said in an email.

The vaccine will be sold under the name Ervebo. It was originally developed by the Public Health Agency of Canada’s National Microbiology Laboratory, a Canadian government research group, and then licensed to NewLink Genetics Corp. Merck acquired the rights in 2014, paying $50 million plus future royalties, and has worked with the U.S. government to develop it further.

Shares of Merck rose 1.6% to $91.41 at 10:46 a.m. in New York. NewLink was up 34% to $2.16 a share.