Developing and bringing to market effective Ebola vaccines requires extreme measures and unprecedented international cooperation, global health experts said on Monday.

In an interim report on a roadmap for vaccines against the current and any future outbreaks of the deadly virus, infectious disease specialists Jeremy Farrar and Mike Osterholm said the scope of effort was "too complex for any single government, organization or company". They called for sustained public-private sector partnership and commitment.

"To bring Ebola vaccines to market, which is clearly in the greater common good given the global consequences of this epidemic, extreme measures are needed to ensure a massive coordinated effort among vaccine manufacturers, government regulatory authorities, government public health agencies, non-governmental organizations and global, national and local leaders," they wrote.

Several potential vaccines are being fast-tracked through development in the hope that one or more may prove able to be used in the world's largest Ebola outbreak in West Africa.

Latest World Health Organization weekly data showed the epidemic has killed 8,235 of the 20,747 people known to be infected worldwide. The vast majority of cases and deaths are in Guinea, Sierra Leone and Liberia.

Two vaccine candidates from GlaxoSmithKline and another from a collaboration between NewLink Genetics and Merck started initial clinical testing in the autumn, while a third from Johnson & Johnson and Bavarian Nordic has just reached the first-in-human testing stage.

The GAVI global vaccines group said last month it would commit up to $300 million to buy Ebola vaccines and will begin procurement as soon as the WHO recommends one.

Yet with case numbers leveling off in the hardest-hit countries, some experts are concerned clinical trials may be slower to report results and political will to see development through may falter.

"Public attention may recede from the current crisis in West Africa, but the likelihood of disease and death from future Ebola outbreaks will not," the interim report said.

"We must not lose sight of the immense contribution that a safe and effective vaccine would make," said Farrar, head of the Wellcome Trust global health charity.

He and Osterholm, director of the University of Minnesota's Center for Infectious Disease Research & Policy (CIDRAP), said success would also provide a model for tackling other deadly infectious diseases, enabling vaccine strategies "to begin without delay in future epidemics".