"This is a major development in the outbreak", said Peter Salama, the WHO's deputy director general of emergency preparedness and response.
The disease caused by Ebola virus was first zafiksirovano Democratic Republic of the Congo (DRC) in urban areas, which may threaten further spread of the disease.
"We are entering a new phase of the Ebola outbreak that is now affecting three health zones, including an urban health zone", Ilunga said, adding he was anxious because Mbandaka is densely populated and at the crossroads of Equateur province.
Mbandaka is about 120 kilometers north of Bikoro, a rural area where the outbreak was first detected.
Officials said there are 44 suspected, probable or confirmed cases of Ebola and that 23 people have died have died so far. The plan is to immunize the more than 500 contacts of infected people in an attempt to stop the virus from spreading.
Ebola, a hemorrhagic disease which is endemic to tropical regions of sub-Saharan Africa, was identified in the 1970s, but historically claimed a relatively small number of lives, despite its mortality rates reaching as high as 50 percent, as its spread between isolated villages and towns was limited.
This Ebola vaccine isn't officially licensed by the US Food and Drug Administration (FDA) yet, seemingly as a matter of the nation's slow and complicated approval process.
Still, while using V920 might not be simple, it has the potential to play a major role in preventing this Ebola outbreak from turning out like the one in West Africa just a couple of years back.
Downstream from Mbandaka is the country's capital, Kinshasa, which is home to roughly 10 million people.
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On Twitter, Lieberman said he had spoken to his U.S. counterpart James Mattis and "updated him on regional developments". Conricus said Israel was not looking to escalate the situation but that troops will continue to be on "very high alert".
They were recorded in Congo's Equateur province.
Isolation zones have been set up in Mbandaka's main hospital as well as Bikoro hospital, with more Ebola treatment centers being set up in Mbandaka and Bikoro.
A 2016 study found it to be 100% effective in trials in Guinea in coordination with the country's Ministry of Health after the 2014-15 outbreak. World Health Organization has sent 4,000 doses to Congo and said it will dispatch thousands more in the coming days as needed.
He said the disease could have been taken there by people who attended the funeral of an Ebola victim in Bikoro, the south of Mbandaka, before travelling to the city.
"The arrival of Ebola in an urban area is very concerning and World Health Organization and partners are working together to rapidly scale up the search for all contacts of the confirmed case in the Mbandaka area", said Dr. Matshidiso Moeti, the WHO's regional director for Africa.
How "experimental" is this Ebola vaccine? It needs to be stored at a temperature of between -60 and -80 C. Electricity supplies in Congo are unreliable.
Many of these people were in remote areas, Salama said. It involves vaccinating contacts of those feared infected, contacts of those contacts, and health care and other front-line workers.
Getting the Ebola vaccine to those who need it won't be easy, though.