Two Ebola patients slipped out of a treatment center this week in the Democratic Republic of Congo, aid agency Doctors Without Borders said, raising fears the virus may spread as health officials raced to trace anyone they may have encountered.
In addition, a targeted vaccination campaign has begun and more than 120 World Health Organization staff have been deployed alongside numerous staff from other organisations, under the leadership of the DRC government. "The quicker patients are admitted, the greater their chance of survival and the greater the chance of limiting the spread of Ebola".
The current outbreak is caused by the Zaire ebolavirus, which has the highest mortality rate, ranging from 60% to 90%, according to WHO. Congo's health ministry has announced there are eight new suspected cases of Ebola.
The other patient was taken home, where he died hours later, leaving health officials scrambling to locate their contacts across the city of 1.5 million people.
The current outbreak, which was officially declared on May 8, began in rural northwestern DRC in a remote location called Bikoro.
Health officials are particularly concerned by the disease's presence in Mbandaka, a crowded trading hub upstream from the capital Kinshasa, a city of 10 million people.
Only this week India has been hit by the brain-damaging Nipah virus, killing 10 people, while Nigeria had its worst Lassa fever outbreak on record earlier this year. About 100 health workers have been vaccinated there as front-line workers face high risk from the virus, which is spread via contact with the bodily fluids of those infected, including the dead. The virus enters the body through broken skin or mucous membranes in the eyes, nose or mouth. Said Berkley: "So the idea that there is only a subset of people who are going to get it is complicated".
Another concern, Salama said, was that five healthcare workers were among those infected.
The UK has acted swiftly to scale up the response to this outbreak of Ebola, a horrific disease which we know has the potential to cause devastating loss of life.
Pharmaceutical giant Merck has provided more than 8,000 doses of its experimental vaccine and will make an additional 8,000 doses available to World Health Organization in the coming days.
"From the moment that they escaped, the (health) ministry, WHO and partners have been following very closely every contact", he said.
Matshidiso Moeti, WHO's regional director for Africa, told AFP she was "very confident" that the United Nations health agency had learned from "the very painful lessons" it received in West Africa.
"The commitment and sacrifice of those on the front line is the most important element of this outbreak", he said.
Large drug companies remain the only realistic vehicles for manufacturing vaccines at scale and the problem of incentivizing them to work on non-profitable diseases in poor countries stretches beyond Ebola.
The countries are the Central African Republic, the Republic of Congo, Angola, Burundi, Rwanda, South Sudan, Tanzania, Zambia and, to a lesser extent, Uganda.
WHO Regional Director for Africa, Matshidiso Moeti, said WHO is helping these countries scale up preparedness so they can detect, investigate, and manage the disease.
But he stressed that not enough had been done to strengthen the "neglected health systems in distress" which permit Ebola to spread. That number could dramatically increase if the disease were to spread widely in a major city.
"One of the challenges is making sure that those messages are really heard and understood in both the health community ... and then certainly in the more general community", Berkley said.
"The next few weeks will really tell if this outbreak is going to expand to urban areas or if are going to be able to keep it under controls", WHO's emergency response chief Peter Salama told ministers and diplomats in Geneva.