A team of researchers from the University of Oxford have calculated the amount of medicine needed to fight the current outbreak of the Ebola virus in Western Africa.
In a study for the World Health Organization (WHO), published in "Nature," epidemiologist Oliver Brady estimates that 30,000 doses of vaccine would have been needed to immunize all of those at risk of infection during the current outbreak.
But the problem is no vaccine has been tested and approved.
Brady's study follows a meeting of experts, organized by the WHO last week, to discuss new ways to confront the disease.
"The expert commission reached the conclusion that it is ethical to use unproven drugs to deal with the outbreak, as long as certain conditions are met," says study author Oliver Brady in an interview with DW.
"The question we tried to answer is: How many drugs would we really need for the current situation?"
Brady and his colleagues compared data from previous Ebola outbreaks and calculated infection risks on that basis.
He warns the demand for vaccines could be higher than the stated 30,000 doses.
"The outbreak shows no signs of waning yet," says Brady. "So we can't estimate what demand might be in the future."
Vaccines for high-risk groups
In their estimate, the researchers assume that all close relatives of patients, medical personnel, undertakers and others in high-risk professions should be immunized.
"We also considered contingency funds, for example for vaccine stockpiles for countries where there is not currently an Ebola outbreak. But there is a high risk that people who might return, for example by air travel, will need treatment upon arrival," Brady says.
Public officials, who are in regular contact with the public, and people who supply medicine to hospitals or participate in emergency programs, should also be consider high-risk.
Preparing mass production
Brady says his study is a call to those who finance, conduct research, and produce Ebola drugs - namely, government and the pharmaceutical industry.
He says they need to step up their efforts to prepare for mass production.
"There are ranges of candidates for both drugs and vaccines in the pipeline amongst a number of manufacturers, prompting this announcement [by the WHO] last week" Brady says. "It is really changing the landscape of what we can do, with what we currently have".
Untested drugs can now be brought into those places where the situation is at its worst, even without prolonged field studies.
But Brady stresses the need to "scale up production."
"It will be relevant for both this outbreak and for future outbreaks," he says.
The ZMapp test
So far, the one untested drug to have shown a potentially significant response in patients is ZMapp.
It was first administered in Liberia to US medic Dr Kent Brantly, whose condition improved, and a missionary.
But stockpiles of the drug are low.
ZMapp consists of a cocktail of three proteins extracted from tobacco plants.
A report in the Frankfurter Allgemeine Zeitung suggests the Fraunhofer Institute for Molecular Biology in Aachen, together with its affiliate in Delaware in the USA, could possibly produce large amounts of the drug.
Brady warns that the effectiveness and potential risks of using untested drugs will only be known once they are used in hospitals.
"Testing its efficacy is very difficult in an emergency situation like this, because the disease is very rare and it is very difficult to conduct any sort of planned clinical trial," says Brady.
But he says the need is very high, and "much higher than it has been for past Ebola outbreaks."
"We do need a solution that produces a huge amount - more doses that can be distributed a lot faster and a lot more equitably."
So we need drugs and vaccines for this outbreak - and the next. Because while there are signs that patients who survive an Ebola infection may develop a certain degree of immunity, it is not something we can rely on.