The World Health Assembly, the governing body of the World Health Organisation (WHO), voted to postpone the destruction of the virus for three more years to allow further research into new anti-viral drugs and vaccinations.

The remaining two samples - held in high security laboratories in the United States and Russia - were due to have been incinerated at the end of next month.

But last month, the US Government announced it would keep the smallpox virus to study new anti-viral drugs and vaccines.

The White House also expressed concern that illegal stocks of the virus might exist and be used some day by insurgent groups as an illegal weapon.

Scientists at the Russian laboratory also spoke out in favour of keeping the virus, saying it could help explain how the human immune system works.

Concerted effort

Smallpox was declared eradicted from the world in 1980, after a concerted international effort by the WHO, ending a scourge that had lasted centuries and killed millions.

Smallpox was eradicated by 1980

Following the decision by the World Health Assembly, a group of virus experts will now be set up to decide an agenda for research.

But the WHO's spokesman on smallpox, Dr David Heymann, says the destruction of smallpox remains a long-term goal.

Smallpox causes the development of blisters on the skin which fill with fluid and become inflamed.

They then burst leaving a foul smelling crust on the skin.

In epidemics, 20% of patients died from the disease. Others suffered disfiguring scars and, occassionally, blindness.

The last case of smallpox was reported in Somalia in 1977.