The patient is 5, and at least two of his family members also have Ebola symptoms.
The outbreak has now reached 2,062 infections, with deaths climbing to 1,390.
The agency highlights earlier case-contact registration and a drastically lower rate of healthcare-related disease spread.
"We get to adapt… and make the response the best we can make it," the WHO's Mike Ryan, MD, says.
Seventeen new infections and 11 new fatalities raise outbreak totals to 2,025 cases and 1,357 deaths.
The groups welcomed new commitments to humanitarian aid, but said a response reset is needed.
An ethics committee fine-tuned an earlier vaccine recommendation, clearing its use in pregnant women past their first trimester and lactating women.
The death rate in infected preschoolers is 77%, compared with 57% for other Ebola patients.
Experts say the outbreak likely began as far back as April 2018 and that nosocomial transmission played a big role in early spread.
The WHO warns that a decline in the rate of cases should be interpreted with extreme caution.
