The Ebola crisis that began in December 2013 killed 11,300 people in Guinea, Sierra Leone and Liberia and has left thousands more survivors with long-term health problems.
The WHO was criticised at the time for responding too slowly and failing to grasp the gravity of the outbreak.
Speaking at an event in the Guinean capital dedicated to individuals who fought to control the disease in their communities, WHO chief Margaret Chan also thanked the Guinean government for its role in developing the vaccine, announced in December, but added a note of caution.
"When this occurs, the world will be far better prepared," Chan added.
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In a major clinical trial using an innovative "ring", or group method, nearly 6,000 people in Guinea were given the test vaccine in 2015, during which not one of them contracted the disease.
Even with an "initially limited" first batch of the vaccine, Chan said, health authorities had another option in their arsenal "beyond isolation and quarantine".
In early 2014, however, a handful of infections in southern Guinea mushroomed rapidly into an epidemic.
Chan emphasised that another positive outcome of the Ebola crisis was renewed focus and funding for vaccines against other contagious diseases, including the fatal Middle Eastern Respiratory Syndrome (MERS) as well as the Lassa and Nipah viruses.
"These significant spillover effects strengthen the world's collective defences against the never-ending threat from emerging and re-emerging infectious diseases," she said.