The epidemic has moved into a new phase, WHO said. The focus has shifted to "ending the epidemic" instead of simply slowing it down. That means concentrating on finding sick people and ensuring they don't spread the virus, instead of building new treatment centers and diagnostic labs.
But getting down to zero cases is still a long way off, Dr. Peter Salama, of UNICEF, said at a press conference Wednesday.
"It is too early to declare a success or a deadline for success," he said. "During the course of this outbreak, we have repeatedly underestimated this pathogen," he added.
Back in April, reported cases plummeted to zero in Guinea for almost a month. Health officials thought the outbreak might be over. They started relaxing. Then the virus came roaring back.
"The key issue that made us fail in the early stages [of this outbreak] ... is we thought we were on top of this," WHO's Ian Norton told Goats and Soda in October.
Guinea recorded only 30 cases last week. But that was actually an increase over the week before, when it had only 20 cases. The virus continues to spread to new regions in Guinea, including parts along the Senegal border.
There's also another logistical problem brewing across West Africa: rain. The wet season begins in April and May. Many parts flood, and some roads wash away.
It will take much longer to get health workers and aid to rural areas during the wet season. So if the epidemic isn't under control by spring, it could last another year, WHO said, instead of possibly months.
To date, there have been more than 22,000 reported Ebola cases in West Africa, with nearly 8,800 deaths.