The Ebola epidemic is now "relatively stable" in Guinea where the latest outbreak first began, but the world is still far from beating the virus.
While there have been some flare-ups in the south-east, things were improving in other prefectures of Guinea, WHO co-ordinator Guenael Rodier told the BBC.
There have been 15, 351 reported Ebola cases in eight countries since the outbreak began, with 5,459 reported deaths. Transmission remains intense in Guinea, Liberia and Sierra Leone, says the WHO, concerned about Mali.
Mali has officially reported a total of six cases of Ebola and six deaths. A massive effort is currently under way to identify all potential chains of transmission, monitor contacts and prevent the outbreak from growing larger, notes the WHO in its assessment report.
At present, 327 contacts have been identified and 310 of these have been placed under daily surveillance.
Intensive tracing and monitoring of the contacts in the first case of a child has failed to detect any additional cases. All 118 contacts, including family members, have now passed through the 21-day incubation period without developing symptoms.
Meanwhile, at a medical centre run by the US Public Health Service staff in Monrovia, a nurse was declared dead, brought to the clinic at a very late stage. The clinic is operated by 69 volunteers of the health service.
Health care workers are at most risk of exposure to the virus.
According to the WHO, 570 health care workers have been infected during this epidemic, and 324 of them have died. More than 100 have died in Sierra Leone.