Later this month, India will be removed from a dwindling list of countries where polio is considered endemic, a huge achievement made possible by people like Madara, a 76-year-old street hawker.

At a temporary immunisation camp in a slum in the northern district of Ghaziabad, 23 kilometres (14 miles) from New Delhi, he is busy at work shepherding boisterous children into queues.

All around, social workers break open tiny bottles containing a polio vaccine, selecting children from the thronging crowd of toddlers and babies and squirting two drops into their mouths.

Madara, a stick-thin resident from a nearby slum, says he began volunteering to help with the vaccination efforts six years ago when he realised he could use his authority as an elderly figure to encourage participation.

"I decided to get involved because I wanted to do something for the future of our children here," Madara told AFP.

Most of the youngsters, whose parents are often rag-pickers or hawkers, live in the nearby tarpaulin-covered homes, a cramped zone of shanties where sanitation and awareness about hygiene is poor.

Polio, which can be deadly and also causes deformed limbs, spreads via the fecal matter of victims, making slums particularly high-risk areas.

Lured by the offer of bright plastic whistles and paper masks, children were keen to leave their homes, forming a disorderly crowd around the vaccinators as they dispensed the drops to infants and under-fives.

India last reported a fresh polio case more than 12 months ago after monumental efforts by millions of social workers and volunteers who have administered 900 million doses of the vaccine in the last year alone.

If all pending lab tests for the virus return negative as expected, the World Health Organisation will remove India from its list of "polio endemic" countries this month, leaving just Afghanistan, Pakistan and Nigeria in this category.

As well as polio camps like this one in Ghaziabad, teams have travelled door-to-door, educating families about the illness and delivering the vaccine.

They have put up makeshift booths in crowded public areas such as train stations, bus stands and markets, and in other locations, including construction sites where they can catch migrant workers and their children.

A "vaccination on wheels" service was rolled out across the north Indian state of Bihar in which social workers jumped on trains and vaccinated all the children onboard.

In 2008, when floods devastated the state, vaccinators were even sent out in boats.

"We had to make a very detailed, dynamic map of the area and send workers in boats to try and get across to stranded families," Lieven Desomer, head of the polio unit at UN children's agency UNICEF in India, told AFP.

As well as the problems of access, the government and international agencies behind the immunisation drive faced problems of ignorance and prejudice.

Vaccinators were attacked, anxious parents would hide their babies from social workers, and there was particular resistance from the Muslim communities in the north of the country.

"There was a general perception that the vaccine was not clean or safe because it came from the West, and that somehow, taking it would make their women and children infertile," UNICEF's Desomer said.

India's crushing summer heat also caused difficulties because vaccines have to be kept at a low temperature to prevent them expiring.

Five years ago, campaigners decided to ensure that vials were only carried in special carriers equipped with ice packs.

Desomer credited "the dogged persistence" of the Indian government for the fall in infections, and said that in 2011 alone, the state contributed 80 percent of the $264 million committed to the fight against polio.

The results of years of innovation, human endeavour, as well as planning and spending, are reflected in the number of infections.

In 2009, India accounted for half of all cases in the world, but infections plummeted to 42 in 2010 and none in the last 12 months.

"It is an amazing achievement. I sometimes feel like I have to pinch myself to make sure I am not dreaming it," Desomer said, while cautioning against premature celebrations.

"We have to remain vigilant and continue immunisations. Complacency at this stage would be a huge mistake," he said.

India will only be judged to have eradicated the disease if it stays polio-free for another two years.