NAIROBI, Kenya — The Ebola outbreak in West Africa, which killed more than 11,300 people over the past two years, officially ended Thursday, according to the World Health Organization.
The U.N. group made its declaration 42 days after Liberia’s last Ebola case was identified — the traditional marker of an epidemic’s conclusion. The other two affected countries, Sierra Leone and Guinea, were declared Ebola-free last year.
Still, the organization warned in a statement that “more flare-ups are expected and that strong surveillance and response systems will be critical in the months to come.”
In recent months, countries such as Liberia have been declared free of Ebola, but new cases were later discovered.
The Ebola epidemic swept through some of the world’s poorest countries with feeble health care systems in 2013 and 2014, infecting hundreds of people before global health agencies mobilized resources.
By then, the disease had spread so widely that villages and cities across a huge swath of West Africa were overwhelmed with cases. Without treatment, many died in the streets or in their homes, widening the circle of infection. As fears spread to the United States that the disease might travel across borders and oceans, potentially wreaking havoc far from West Africa, the U.S. government allocated $5.4 billion in emergency Ebola funding.
On Tuesday, in his State of the Union address, President Obama commended physicians and development workers who helped stop the spread of the virus.
“They set up the platform that then allowed other countries to join in behind us and stamp out that epidemic. Hundreds of thousands, maybe a couple million lives were saved,” Obama said.
But critics say that the United States, like much of the international community, was late in delivering a robust response in West Africa. By the time it had constructed more than a dozen Ebola treatment centers in Liberia, for example, the disease was already fading away, and some of those centers sat empty.
With Thursday’s official announcement that the Ebola’s transmission had ended, global health officials acknowledged the achievement — and the unprecedented challenged posed by the disease.
“Detecting and breaking every chain of transmission has been a monumental achievement,” said Margaret Chan, WHO’s director general. “So much was needed and so much was accomplished by national authorities, heroic health workers, civil society, local and international organizations and generous partners.
“But,” she added, “our work is not done and vigilance is necessary to prevent new outbreaks.”