An experimental vaccine against the Ebola virus was found to be 100% effective, according to a study published in The Lancet on Thursday.

The results offer hope of better protection against the disease that ravaged West Africa in 2014, killing more than 11,000 people.

“Ebola left a devastating legacy in our country. We are proud that we have been able to contribute to developing a vaccine that will prevent other nations from enduring what we endured,” said Dr. KeÏta Sakoba, the director of the national agency for health security in Guinea.

The vaccine

The experimental vaccine was given in 2015 to people in Guinea who were in contact with patients who had recently confirmed cases of Ebola.

A few months after the early trials, the World Health Organization said the preliminary results were an “extremely promising development.”

While the study’s participants were initially randomized, the process was stopped after initial results in order to get the vaccine to those in need.

The trial involved more than 11,000 people, according to the WHO, which led the trial in conjunction with Guinea’s Ministry of Health.

A total of 5,837 people were given the rVSV-ZEBOV vaccine, and none had a recorded case of Ebola after 10 days or longer, the study says.

Among people who were not immediately given the vaccine, there were 23 cases.

Some people who had the vaccine reported headaches, fatigue and muscle pain. Two patients had serious reactions, including one who had an allergic reaction.

Ring strategy

Ebola was first discovered in 1976, and before the 2014 outbreak, it typically hit isolated African communities — those outbreaks were much more manageable for medical teams to parachute in and treat patients.

But the virus reached cities in 2014, spreading like wildfire and catching the global health community off guard.

Ebola is highly contagious once patients are symptomatic, so as families and close-knit communities tried to care for sick loved ones, they risked infection.

To combat this, researchers doled out the vaccine to so-called “clusters” or “rings” — groups of people who had been in contact with an Ebola patient.

It’s the same strategy that was used to eradicate smallpox.

“The premise is that by vaccinating all people who have come into contact with an infected person, you create a protective ‘ring’ and stop the virus from spreading further,” John-Arne Rottingen of the Norwegian Institute of Public Health, which has been involved in implementing the trial, told CNN last year.

The vaccine was manufactured by Merck, Sharp & Dohme and is being fast-tracked by US and European regulatory agencies.

Merck has promised to ensure that 300,000 doses of the vaccine will be available in case of a new Ebola flareup. It will submit the vaccine for licensing by the close of 2017.