Polio is still a problem in Pakistan. (Source: BBC)

The World Health Organization has declared its South East Asia region polio-free.

The certification is being hailed a "historic milestone" in the global fight to eradicate the deadly virus.

It comes after India officially recorded three years without a new case of polio.

The announcement means 80% of the world is now officially free of polio, although the disease is still endemic in Afghanistan, Nigeria and Pakistan.

Other countries in the WHO South East Asia region, such as Sri Lanka, Maldives and Bhutan, have been free of the virus for more than 15 years.

However, despite the "huge global significance" of the announcement, the WHO admits there are still major challenges to overcome if the world is the reach the goal of eradicating polio everywhere by 2018.

There have also been outbreaks in conflict-hit countries such as Syria, which had previously managed to stamp out the virus.

Polio mainly affects children under five years old. The virus is transmitted through contaminated food and water, and multiplies in the intestine. It can then invade the nervous system, causing paralysis in one in every 200 infections.

South East Asia is the fourth of six WHO regions to be declared polio-free after the Americas, Western Pacific and Europe regions. Eastern Mediterranean and Africa have yet to gain a similar status.

(Source: BBC)