The World Health Organization plans to say on Monday that India has gone exactly three years since recording its last polio case, one of the biggest public-health achievements of recent times, and one that could set the stage for stamping out the ancient scourge globally.

Public-health officials now hope to officially certify India as polio free in coming weeks.

Many long doubted that India could pull it off, given the country's size, poor sanitation and the enormous challenge of vaccinating millions of children, often in far-flung places and in the face of societal and religious resistance.

"India was by far the hardest place in the world to get rid of polio," said Bill Gates, chairman of Microsoft Corp. and co-chair of the Bill and Melinda Gates Foundation, a major financial donor in the global polio campaign. "It's quite phenomenal they did it."

The success with polio has also emboldened India to announce that it will now try to eliminate measles as well. At the same time, India faces significant public-health challenges such as malaria, HIV/AIDS and the spread of drug-resistant tuberculosis. In epidemiology, elimination of a disease means wiping it out regionally, while eradication gets rid of it globally.