The World Health Organization (WHO) formally declared India polio-free Thursday, as there have been no new cases in three years.

The announcement means that 80 percent of the world is rid of the crippling disease, excluding Afghanistan, Nigeria and Pakistan, where it is still endemic.

India's last case of the contagious polio virus was detected in January 2011 in a 2-year-old girl in the state of West Bengal.

This is "a day that we have dreamt about," Poonam Khetrpal Singh, a WHO Southeast Asia official, said at a ceremony in New Delhi, according to The Associated Press.

"It is a day that all countries fought hard for, and a day when all stakeholders come together to celebrate the victory of mankind over a dreaded disease that, for centuries, has killed and disabled legions," he told the Thomson Reuters Foundation.

Polio is a vaccine-preventable disease that attacks the central nervous system and can cause irreversible paralysis within hours of infection. The virus spreads in areas of poor sanitation through contaminated food or water, with children under 5 years old most susceptible.

In 1988, the Global Polio Eradication Initiative was launched to wipe out the disease in endemic nations. At the time, more than 350,000 children across 125 countries were being paralyzed or killed by polio annually - a number than has since dropped by 99.9 percent.

India proved to be especially difficult, with more than 50,000 children contracting the virus each year. But now thanks to immunizations, over 170 million children are vaccinated.

South East Asia is the fourth of six WHO regions to be declared polio-free after the Americas, Western Pacific and Europe regions. But WHO says the fight against polio still isn't over.

"Every child in the world is at risk of contracting polio until such a time as the wild polio virus is completely eradicated from every part of the world," Deepak Kapur, of Rotary International's India National Polio Plus Committee, told BBC News.