A vaccine to protect millions from the Ebola virus decades after it was first detected does not exist because the disease previously only affected poor African nations.

The head of the World Health Organisation's scathing conclusion came as nearly 5,000 people have lost their lives to the hemorrhagic fever - the majority in Sierra Leone, Liberia and Guinea.

Dr Margaret Chan, director general of the WHO, criticized drugs companies for turning their backs on 'markets that cannot pay', The Daily Mail reported.

She said the current outbreak - the most deadly in history - has exposed two WHO arguments 'that have fallen on deaf ears for decades'.

Addressing the regional committee for Africa in Benin yesterday, Dr Chan said: 'Ebola emerged nearly four decades ago. Why are clinicians still empty handed, with no vaccines and no cure?

'Because Ebola has historically been confined to poor African nations.

'The R&D (research and development) incentive is virtually non-existent.

'A profit-driven industry does not invest in products for markets that cannot pay.

'WHO has been trying to make this issue visible for ages. Now people can see it for themselves.'

She highlighted an 'urgent need to strengthen long-neglected health systems', in Africa.