But despite the promise of those tightening time frames, the global health agency's point person for Ebola vaccines and drugs warned that vaccine is not a magic bullet that will stop the unprecedented West African outbreak.
Dr. Marie-Paule Kieny, WHO's assistant director general for health systems and innovation, said a few hundred thousand doses of the two main candidate vaccines will be available in the first half of 2015 and will be used in large clinical trials. Efforts to vaccinate the general public in the affected countries won't start before June — if such a approach is undertaken at all.
Trials may begin as soon as late December in Liberia, Kieny said during a media briefing on an international vaccine summit the WHO held on Thursday. Companies making vaccines, countries that are likely to help pay for them and other key players such as Medecins Sans Frontieres, the Gates Foundation and the World Bank attended the meeting.
Kieny said it's not currently clear if both vaccines will be ready to be rolled out in efficacy trials — studies that show if a vaccine works to protect people — in December. The Canadian-made vaccine, VSV-ZEBOV, is slightly behind the other leading candidate in safety testing. This means the trial may start with the other vaccine, made by GlaxoSmithKline, and the second arm will be commenced a bit later.
While she revealed that efforts to further compress the time to use of the vaccines are continuing, Kieny also injected some cautionary notes into her messaging.
"Vaccine is not the magic bullet. But when ready, they may be a good part to turn the tide of this epidemic," she said from Geneva.
Her comment was echoed in remarks from Dr. Jeremy Farrar, director of Britain's Wellcome Trust, a charity which is funding many of the clinical trials.
"A safe and effective Ebola vaccine alongside a massive increase in classic public health measures could make a transformative contribution to containing this epidemic," Farrar said in a statement.
"It is vital to prioritize testing, production and deployment of all the viable candidates. It is thus hugely encouraging that industry, national governments, philanthropy, regulators and the WHO are now collaborating with urgency to fast-track trials, manufacturing and deployment."
Earlier this week the CEO of NewLink Genetics — the U.S.-based company that holds the licence for the Canadian-made vaccine — told The Canadian Press his company may have between 700,000 and seven million doses of vaccine by the end of this year.
Dr. Charles Link said the final figure would depend on how much vaccine — or how little — must be given to each person to achieve protection. That information will be established by the safety studies currently underway.
Asked about the discrepancy between the numbers she cited and Link's projections, Kieny suggested for planning purposes it is more prudent to go with figures that appear realistic rather than ones that are more ambitious.
"It's better to be really realistic in what we say. I'm not saying that NewLink will not happen. But I'm giving numbers that I think in all likelihood will be there."
She said there is much uncertainty at this point about how much vaccine will be required for each dose of the NewLink product, "so the forecasting is much more dicey."
Health-care workers and people who work on the safe burial teams are expected to be among the first to receive vaccine in the clinical trials. It remains unclear whether mass vaccination of the populations of these countries will be undertaken, Kieny said.
"If the vaccine is proven effective and the epidemic curve is justifying ... mass vaccination and if the vaccine is available in enough quantity, then there might be mass vaccination," she stressed.
"But again, this is with three conditions: that it is safe and effective, that the epidemic curve justifies that something like that should be done and the third, that there would be enough doses available.''
The second condition — that the epidemic curve justify mass vaccination — would be met if the combined other containment methods were not slowing the spread of the virus by the time large amounts of vaccine are available.
Kieny said planning for large clinical trials is furthest advanced in Liberia, which is why the work will start there. Work is also progressing to do clinical trials in Sierra Leone but is trailing in Guinea.
Sources who have attended this and other recent meetings at the WHO on Ebola say the response is shaping up along geopolitical lines, with the United States — where the GSK vaccine was created — leading the response for Liberia. Britain has stepped up to shepherd efforts in Sierra Leone and France is taking the lead in Guinea.
On the issue of who will pay for the vaccines, Kieny said MSF — also known as Doctors Without Borders — volunteered to create a vaccine fund. And the British government offered to set up an indemnification fund to cover the cost of any claims against the vaccines makers, if adverse reactions occur.
Follow @HelenBranswell on Twitter.