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.
"Scientists do not yet know exactly where in nature the Ebola virus hides between outbreaks, but nearly all experts agree that another outbreak is inevitable," she said, speaking to an audience of scientists, Ebola response coordinators and dignitaries.
"When this occurs, the world will be far better prepared," Chan added.
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.
First identified in 1976 in what is now the Democratic Republic of Congo, the Ebola virus erupted periodically in outbreaks of up to a couple of hundred cases, mainly across west and east Africa.
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.
Also speaking at the event, President Alpha Conde said it was "time Africa benefited from cutting-edge technology, notably in the field of biomedical sciences," and called on industrialised nations to share their expertise.