In an important milestone, Ebola epidemic that killed over 11,000 people and triggered a global health alert for the last two years has died down in West Africa with WHO today declaring Liberia, the last affected country, free of the deadly virus disease.
The WHO, however, cautioned that it was too early to fully declare an end to the epidemic globally as residual infections may start flare-ups again because virus can persist in survivors for up to a year and be transmitted through sex and other means.
Liberia, which along with Sierra Leone and Guinea was an epicenter of the latest outbreak, was first declared free of the disease last May, but new cases emerged two times.
The latest flare-up was in November last year which killed a boy.
"Today is a good day. It is an important day. Today, WHO declares the end of the most recent outbreak of Ebola Virus Disease in Liberia. The outbreak that is associated with the flare up of cases mid-November," said Dr Rick Brennan, Director of WHO's Department of Emergency Risk Management and Humanitarian Response.
"It is also the first time that all three countries in West Africa -- Guinea, Sierra Leone and Liberia -- have stopped all known chains of transmission of the disease since the outbreak started in 2014," he added.
A country is declared to be free of human-to-human transmission once two 21-day incubation periods pass since the last known Ebola case has tested negative for Ebola twice.
The UN health agency, however, warned that Ebola flare-ups as a result of the virus persisting in the semen of male survivors for up to 12 months could pose a residual for more flare-ups as people return to a "new normal".
"While this is an important milestone and a very important step forward, we have to say that the job is still not done," said Brennan.
The WHO called the risk of a flare-up in "relatively low" but "significant".
"We have had ten of these flare-ups and we are anticipating more," said Brennan.
There have been four flare-ups in Liberia, three in Guinea and three in Sierra Leone after the three West African nations were declared Ebola-free by WHO at different points in time.
The flare-ups are, on an average, 27 days apart.
"It's a new normal. It's a normal where Ebola has been added as a very serious disease to a number of other diseases that also affect the populations," said Peter Graaff, Director of the Ebola response team in Geneva, referring to how embedded the disease had become in these societies.
As part of the efforts to manage these residual risks the WHO is considering the use of the Ebola vaccines to vaccinate the intimate partners of the survivor male population as a clinical trial.
The outbreak of Ebola which may have started as early as December 2013 was the most complex and deadliest outbreak of the disease which put the lives of 22 million people across Liberia, Sierra Leone and Guinea at risk.
"The disease did get away from us all collectively," said Brennan referring to the slow response of the WHO and other international organisations at the start of the epidemic which eventually killed more than 11,000 people and affected 28,300 people across the three countries of West Africa.