With worries about the disease spreading in Mbandaka, the WHO said the DRC risk is very high and the regional risk is high.
More than $25 million is newly pledged for an outbreak that has grown to 51 total cases, 28 confirmed.
Four more illnesses have been reported, along with another death in a healthcare worker.
"At this point, it's not cost beneficial to declare an international state of emergency," a WHO official said of the 45-case outbreak that has killed 25 people.
"This is a concerning development" the WHO director-general says.
The WHO says participation in the ring vaccination efforts will be voluntary.
In addition, the WHO is eyeing a ring vaccination strategy to reach those most at risk.
The DRC now has 2 confirmed, 25 probable, and 12 suspected cases—39 total.
The outbreak area covers 37 miles of rough, difficult-to-access terrain.
The WHO said, of 21 cases, 17 have links to other cases and 3 are in health workers.
