An independent panel of 19 specialists has called for sweeping reforms to ensure there is no repeat of the catastrophe, which killed more than 11,000 people.
Their main criticism was the WHO's failure to respond quickly when the disease first emerged in Guinea.
Internal memos seen by the panel showed that the WHO was reluctant to declare a public health emergency because it did not want to upset African dictators and feared it would be criticised if the outbreak turned out to be mild, like the 2009 H1N1 pandemic.
"The long-delayed and problematic international response to the outbreak resulted in needless suffering and death, social and economic havoc, and a loss of confidence in national and global institutions," the panel concluded.
Meanwhile, Ebola has returned to Liberia, with three cases confirmed in one family, two months after the country was declared free of the virus - for the second time - and days after the last country affected in West Africa, Guinea, cleared its last case.
