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.
In the past 5 weeks, 21 cases of viral hemorrhagic fever have been reported in the area, 17 of them fatal.
The Saudi Arabian Ministry of Health (MOH) recorded a new case of MERS-CoV yesterday in Sakakah, a city in the northwestern corner of the country.
