(CNN) -- India has been certified polio-free by the World Health Organization after going three years without an endemic case of polio. The eradication of polio in India is heralded as one of the biggest achievements in global health efforts.

The polio-free certification by the Regional Certification Commission came Thursday, along with a proclamation that Southeast Asia is free of the disease.

Just five years ago, India was home to nearly half the global polio cases and considered one of the most technically difficult places to eradicate the disease, because of sanitation challenges and high-density population.

India's last case was reported in a young girl paralyzed by polio in West Bengal in January 2011.

Meet the last person to have polio in India

So how did the second most populous country in the world, considered the hardest place to end polio, become free of the disease?

Health workers determined that the children of migrants or those growing up in difficult-to-reach areas were not getting access to vaccines. So they deployed immunization efforts to reach the most vulnerable, according to UNICEF.

India launched a massive effort involving a surveillance network and almost 2.3 million vaccine administrators, who identified communities falling through the cracks.

To counter rumors and misgivings about the vaccine, social mobilizers, religious leaders and parents were included to increase understanding about immunizations.

They also bolstered communication and outreach efforts that often included Bollywood celebrities and cricket players. The efforts combined government, various U.N. agencies as well as philanthropic organizations.

The highly infectious viral disease primarily affects young children and could lead to paralysis and death. It can be prevented through immunization, but there is no cure.

The incidence of the disease has dropped by more than 99% since 1988. It remains endemic in three countries -- Pakistan, Nigeria and Afghanistan -- down from more than 125 countries in 1988.

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Polio workers in those countries have been facing violence as some militant groups have begun targeting anti-polio campaigns.

In December, the WHO began vaccination efforts to reach more than 23 million children across the Middle East following an outbreak of the disease in Syria.