A global vaccine coalition official said on Thursday that cases so far identified in the Congo Ebola outbreak represent just the top of the iceberg and it may be hard to develop a safe, effective vaccine within a target time of three months.

The outbreak in eastern Democratic Republic of Congo encompasses 600 suspected cases and more than 130 suspected deaths so far, with the World Health Organization declaring it a public health emergency of international concern.

"I have described this outbreak as being like an iceberg, we've seen the top of the iceberg, the top, as we get closer to it, is pretty large," said Jane Halton, chair of the Board of the Coalition for Epidemic Preparedness Innovations (CEPI).

"REAL NUMBERS ARE MUCH BIGGER"

"We are now into the many hundreds of cases and hundreds of deaths, but the truth of the matter is that real numbers are much bigger than that," she told a briefing by the ACANU press club in Geneva.

CEPI, which funds development of new vaccines and is looking at potential candidates for Ebola, has set the goal of having a safe, effective vaccine for major outbreaks within 100 days.

"Possibly, it's a big lift," Halton responded when asked if it would be possible to achieve that target, adding, "I can guarantee you that we will be in a position to respond faster than we would have been five years ago."

She declined to give a timeframe, however. 

Unlike with the more common Zaire strain of Ebola, there are no approved virus-specific ​therapeutics or vaccine for the Bundibugyo strain, which has previously proved less lethal.

Halton said work to gather antibodies had begun before the outbreak and a shot against the Bundibugyo strain was set to be the "next cab off the rank" for development before the outbreak.

"It is regrettable," she said regarding the timing, adding that it was a "very difficult position".

With a number of early-stage vaccine candidates work was being done to speed preclinical safety tests with the aim of running a trial in the current outbreak, she added, provided local communities give informed consent.