Officials face difficult choice as they decide which patients are to receive experimental drug that could prove life-saving, ineffective or harmful

The number of Ebola victims in west Africa may “vastly underestimate the magnitude of the outbreak”, the World Health Organisation has said.

With more than 1,060 deaths and 1,975 sufferers, the Ebola outbreak is already the deadliest ever and the UN health agency says it is prepared for the crisis to continue for months.

Liberian officials faced a difficult choice – deciding which handful of Ebola patients would receive an experimental drug that could prove life-saving, ineffective or even harmful.

ZMapp, the untested Ebola drug, arrived in the country on Wednesday. A day later, no one had yet received the treatment, which officials said would go to three people.

The outbreak, which was first identified in March in Guinea and since spread to Liberia, Sierra Leone and Nigeria, has overwhelmed the already strained health systems in west Africa and raised questions about whether authorities are doing enough to respond.

There is no licensed treatment for Ebola, a virus transmitted by contact with bodily fluids, so doctors have turned to the limited supply of untested drugs to treat some cases.

The Liberian government had previously said two doctors would receive ZMapp, but it was unclear who else would. Information minister Lewis Brown said it would probably be another healthcare worker. These are the last known doses of ZMapp left and the San Diego, California-based company that developed it has said it will take months to build up even a modest supply.

The outbreak has sparked an international debate over the ethics of giving such untested drugs to the sick and of deciding who should get them. So far, only two Americans and a Spaniard have received ZMapp. The Americans are improving, but it is unclear what role the drug has played. The Spaniard died within days.

Now Liberian officials are facing those questions. In this outbreak, over 50 per cent of those who contracted Ebola have died, according to the UN health agency.

“The criteria of selection is difficult, but it is going to be done,” said Moses Massaquoi, the doctor who helped Liberia obtain the drug from Mapp Biopharmaceutical.

“We are going to look at how critical people are. We are definitely going to be focusing on medical staff.”

He said people past the “critical phase” who looked likely to survive would not be chosen.

Massaquoi said there was only enough of the drug to treat three people. Treatment will be staggered, so doctors can observe the effects in one patient before moving on to the next.

Arthur Caplan, director of medical ethics at NYU Langone Medical Centre, said the choice of who to treat would have to balance helping the largest number of people with learning the most from the treatments.

He said the question was not “whose life do we save?”, but “who gets the chance to be experimented on?”

For that reason, recipients need to be good experimental subjects ­– people who have recently contracted the disease and are more likely to respond to treatment or perhaps younger patients, he said.