There is a basic rule in the pharmaceutical industry: developing an effective vaccine or drug takes about ten years.

This period of time is calculated from basic research in test tubes and animal experiments to the point of clinical trials in humans and the final approval to gain a license.

With Ebola, it will presumably not take years to find a vaccine because researchers don't have to start from scratch.

Scientists have been working on Ebola vaccines for quite some time. They have already identified several vaccine candidates and have tested them in animals, even in apes.

Only human trials are missing. But they are already underway or scheduled to start soon.

Safety comes first

The World Health Organization announced on Tuesday it hopes to begin testing two experimental Ebola vaccines on health-care personnel in West Africa by January.

WHO's spokeswoman Fadela Chaib said the agency expects 20,000 vaccinations in January and similar numbers in the months after that.

Before the real-world testing in Africa can start, though, the vaccines have to prove safe. It has to be made sure that the vaccines do not cause any dangerous side effects.

Moreover, trials in healthy humans have to show that the vaccines do indeed trigger an immune response: the test person should start producing antibodies against the Ebola virus.

These phase 1 clinical studies are already underway in healthy volunteers in Africa, the US and Europe, including Germany.

The World Health Organization hopes to have these safety data available in December.

According to the agency's timetable, subsequent phase 2 studies are to be "approved and initiated in affected and non-affected countries" in January and February 2015.

Phase 2 studies include persons who are in contact with the virus. These trials will have to show that the vaccine works.

Normally, a phase 2 study involves no more than 100 to 500 patients. Phase 3, which involves up to several thousand people, is started only if phase 2 was successful.

The World Health Organization apparently plans to rush forward and extend phase 2 to thousands of people. That means that phase 3 wouldn't be needed at all.

Two promising candidates

The two most advanced Ebola vaccine candidates are cAd3-EBO and VSV-EBOV.

cAd3-EBO is being developed by the US National Institutes of Health and the pharmaceutical company GlaxoSmithKline.

It consists of a chimpanzee-derived cold virus with an Ebola virus gene inserted.

"Development of the vaccine candidate is progressing at an unprecedented rate, with first phase 1 safety trials with the vaccine candidate underway in the USA, UK and Mali, and further trials due to start in the coming weeks," GlaxoSmithKline writes on its website.

GSK says it acquired this Ebola vaccine candidate through the acquisition of the Okairos biotechnology company in May 2013.

According to Glaxo Smith Kline, the vaccine is being manufactured at a plant in Rome.

The other vaccine candidate, VSV-EBOV, was developed by the Public Health Agency of Canada. It has been sent to the US Walter Reed Army Institute of Research in Maryland for testing on healthy volunteers.

The vaccine uses a weakened virus, which infects livestock: the vesicular stomatitis virus. One of its genes has been replaced by an Ebola virus gene.

Researchers began testing the potential vaccine on October 13, the Walter Reed Army Institute of Research announced. "The trial's focus is safety but scientists are also evaluating the immune response to the vaccine," they said.

No guarantee

WHO Assistant Director-General Marie Paule Kieny acknowledged on Tuesday there were many "ifs" remaining and "still a possibility that it [a vaccine] will fail."

Even if both vaccine candidates were successful in animals and could protect them from the disease, it doesn't automatically follow that it will also work in humans.

Health expert also stress that a vaccine alone won't stop the outbreak.

There probably won't be enough doses available in the beginning, although a GlaxoSmithKline spokesperson said GSK is "seeing what we can do to ramp-up production to a commercial scale."

WHO's Kieny said the first persons to receive a dose would be health-care workers in Ebola treatment centers.

They are particularly at risk to catch the virus, and more than 200 of them have already died of the disease.

Doctors without Borders urged pharmaceutical companies to speed up their work.

"A vaccination could prevent further spread of the virus and obviate future outbreaks," the organization writes on its website.

All you need is money

Critics of the pharmaceutical industry see this sudden rush for a vaccine as a proof that we could have many more vaccines and drugs if only the clinical trials were being pushed further.

"If this [Ebola] was a disease in developed countries where there was a commercial market for the product, one of these vaccines would now be licensed, there is no doubt," Peter Walsh of the University of Cambridge told DW earlier this year, before the Ebola epidemic in West Africa began.

Walsh developed a promising Ebola vaccine in apes that could be effective in humans, he said - just like many other research groups have already done.

"It is not a technological question to develop a vaccine that works; we just don't have the money to do it."

Clinical trials are the most expensive part of drug development.

"That the recent trials weren't done in the past is due to the low economic incentive for private companies to develop an Ebola vaccine," Doctors without Borders write on their website. "Before this epidemic, the disease affected only relatively few people in poor countries."

The fact there are any vaccine candidates at all, they say, is because governments want to protect themselves from potential bioterrorism.