There is no licensed vaccine for the Ebola virus, but a promising candidate vaccine could be deployed within a matter of days if the DRC government gives its approval, the WHO said.
"The preparations are in place. We could potentially mount a campaign within around a week given all of the conditions... are met," Peter Salama, the agency's health emergencies chief, told reporters during a conference call.
Last week DRC declared an outbreak of the highly contagious disease, the eighth to date in a sprawling country five times the size of France.
So far, two cases of the virus have been confirmed in a laboratory while 18 others are suspected in the remote Bas-Uele province, an equatorial forest zone near the Central African Republic.
Three of those people have died, including the first known case: a 39-year-old man who died on the way to hospital in Likati on April 22, suffering from fever, vomiting and bleeding symptoms.
A person caring for him and the motorcycle driver transporting him also died, Salama said.
This is the first outbreak of Ebola, which spreads by contact with bodily fluids, since the west Africa epidemic that ended in January last year after making nearly 29 000 people ill and killing more than 11 300.
During that epidemic, a vaccine made by US pharmaceutical giant Merck was successfully tested in hard-hit Guinea.
As in that test, the WHO would like to do a ring-trial in DRC, meaning the vaccine would be given to all people who have had contact with known cases, as well as those who have had contact with those people.
Health workers would also be given the vaccine.
In addition to waiting for an official invitation from Kinshasa, there are a number of logistical challenges to rolling out a trial.
For starters, the vaccine needs to be stored at minus 80 degrees Celsius, which could be more than tricky in Likati, which is 1 300km from the capital.
"As you can imagine, in an area without telecommunications, without road access, without large-scale electrification, this is going to be an enormous challenge," Salama said.
But he said huge efforts were under way to overcome the challenges.
The WHO, which faced crushing criticism for taking too long to sound a global alarm and to scale up its response to the epidemic that ended last year, emphasised the quick response since DRC declared the latest outbreak on May 12.
Airplanes and helicopters are being used to bring in health teams, who have already managed to track down more than 400 people who have had contact with the known cases, Salama said.
An Ebola treatment centre has also been set up at the Likati hospital and teams are working on deploying a mobile laboratory to help speed up diagnoses, he said.
The WHO meanwhile remains "optimistic" that Kinshasa can rapidly bring the outbreak under control, the agency's regional chief for Africa said during the conference call.
"DRC has extensive experience in... controlling Ebola outbreaks," she said.
Salama also said the risk of the outbreak spreading internationally was low.
But he added: "We have also learned never, ever to underestimate the Ebola virus diseases, and we will be remaining vigilant."