British scientists have said that up to 30,000 people could have used experimental treatments or vaccines so far in the world’s worst outbreak of Ebola currently plaguing West Africa.

The calculation highlights the dilemma facing officials considering how to distribute the tiny quantities of unproven drugs that are likely to be available in the near term to fight the deadly disease.

The World Health Organisation (WHO) is hoping for improved supplies of experimental treatments and progress with a vaccine by the end of the year, after last week backing the use of untested drugs and vaccines.

Oliver Brady, an epidemiologist at the University of Oxford, and colleagues have been crunching the numbers and believe the number of people needing such treatment or protection is very large, even under a conservative scenario.

One rare experimental drug, ZMapp, has already been used on two American aid workers and is now being given to three African healthcare workers who showed symptoms of the disease, all of whom have shown very promising signs of recovery.

But California-based Mapp Biopharmaceutical, which makes the drug, has said its scarce supplies are now exhausted and producing more will take time. It is currently working with Kentucky BioProcessing and the U.S. government to accelerate scaled-up production.

There are other drugs in the pipeline but all are unproven and have yet to clear even the earliest stage of clinical trials. Brady said available stocks were limited to treatment courses for tens or at most hundreds of people.