After two harrowing years of beating back Ebola in communities across west Africa the nightmare is finally, officially over, the World Health Organization declared today. Until now Liberia was the lone country waiting for the all-clear from WHO, and it now has reached the 42-day disease-free designated cutoff—twice the incubation period of the virus.

Ebola halted daily life, ravaged families and derailed the economies of Liberia, Guinea and Sierra Leone since its first known appearance in December 2013 in a remote area of southeastern Guinea. A confluence of events including a porous border between Guinea and its neighboring countries helped the pathogen go on to kill more than 11,300 people and infect more than 28,000. During the height of the epidemic, schools in affected regions were closed, vaccinations against other diseases halted and goods no longer made their way to markets. Yet still researchers are not completely sure of the virus’s origins or its many intricacies. WHO cautions that west Africa is still at high risk of additional small outbreaks of the disease. “Ebola virus is likely still present in the region, hidden both in bats, the likely natural reservoir, and in some humans,” says Daniel Bausch, a physician on WHO’s Clinical Care Team for Ebola. 

Liberia, the country hardest hit by Ebola, had been declared Ebola-free twice—in May 2015 and September 2015—only to have the virus resurface within its borders soon after. In that country of about 4.2 million people more than 4,800 individuals died from the disease since 2014. The WHO announcement today, however, marks 42 days since the last Ebola patients in Liberia tested negative twice. Guinea was declared Ebola-free last month and Sierra Leone reached its 42-day mark in November 2015.

Now, the long slog to help Ebola survivors and their communities continue the recovery process continues. According to available estimates, more than half of Ebola survivors continue to suffer from lingering symptoms including muscle pain, headaches and visual problems that may hamper their ability to return to their jobs and activities of daily living.

Although enormous strides were made to break all the chains of disease transmission that led to this historic day, health workers will still have to carefully monitor survivors and their contacts to ensure that no further flare-ups occur. “Recent findings reveal that Ebola virus can persist perhaps up to a year after recovery in some of the body's immunologically protected sites, that is, sites that that are hard for the immune system to reach,” says Bausch, referring to semen, fluids in the eye, brain, spinal cord and inside the uterus or fetus of women who became infected with Ebola while pregnant. “Transmission from survivors is rare, and there is no risk from casual contact, but we nevertheless cannot become complacent.” WHO plans to continue monitoring Liberia for the next 90 days to ensure that if any new cases crop up, they are quickly identified and their contacts are closely monitored.