The last patient tested negative for the Ebola virus in Liberia, making all three West African countries hardest hit by the outbreak to be free of the disease, the World Health Organization announced Thursday. Though the agency warned that more flare-ups were possible.
WHO said all known chains of transmission have ended in Sierra Leone, Guinea and Liberia, nearly two years after the latest Ebola outbreak was first recorded in a small Guinea village.
To date, the Ebola outbreak has claimed more than 11,300 deaths and infected more than 28,500, WHO said.
“Detecting and breaking every chain of transmission has been a monumental achievement,” Margaret Chen, WHO director-general, said in a statement released Thursday. “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 Chan added that the organization’s “work is not done and vigilance is necessary to prevent new outbreaks.”
According to the Centers for Disease Control and Prevention, the Ebola virus can linger in survivors, such as in their spinal fluid, eyes or in the semen of males, for up to a year.
WHO declared Sierra Leone Ebola-free in November and Guinea in December, but the disease reemerged in Liberia on Nov. 24, when a 15-year-old boy died from the disease. Liberia was previously twice declared free of Ebola in 2015. Thursday’s announcement came 42 days, or two incubation periods, after that fresh round of infections.
WHO said there have been 10 Ebola flare-ups, similar to the recent one in Liberia, sometimes long after survivors were successfully treated for the disease.
WHO said it plans to step up its surveillance and response capabilities, a move that will be “critical” in the coming months. However, WHO director Rick Brennan said there was a “general acknowledgement” that the organization had a slow reaction to the first signs of the outbreak, the Associated Press reported.
In 2014, the AP obtained an internal WHO document that said “[n]early everyone involved in the outbreak response failed to see some fairly plain writing on the wall… A perfect storm was brewing, ready to burst open in full force.”