After 20 minutes navigating the foetid alleyways of Old Delhi's market looking for someone to mend the broken winder on my watch (repair cost: 65p), I was picking my way through the river of humanity flowing down Chandi Chowk, the main shopping street, when a man perched on a toy trike emerged from the crowd and hurtled down a steep kerb straight towards me, grinning crazily. As I dodged and glanced down I glimpsed a pair of twisted limbs sticking out at an impossible angle, ready to fell all comers.

Was he a polio victim? Almost certainly. Many of those who crawl along the city's streets dragging useless limbs, begging for alms certainly are. They are a living memorial to a disease already banished from the West – and a warning of what lies in store should it ever return.

In the early 1990s there were 3,000 cases of paralytic polio each year in India. Now there are none.

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In a country of 1.2 billion people, the monumental scale of that achievement – successfully vaccinating 95 per cent of children aged five and under – is a tribute to Indian diligence. India's passion for bureaucracy may burden businesses with paper work (and drive visa applicants to despair) but here has proved it can also save lives.

The centrepiece of the campaign is the national immunisation days (NIDs), begun in 1995, around which all other activities are organised. The aim is to vaccinate 172 million children under five on a single day, employing 2.5 million vaccinators who are moved in 155,000 vehicles (including boats, elephants and camels) carrying over six million ice packs (to keep the vaccine cool) and supplying over 700,000 vaccination booths – set up in hospitals, on street corners and out of the back of cars. The NID is followed by a five day mop up phase in which vaccinators move from house to house, following a meticulously planned route, seeking out those missed.

The task is a logistical nightmare. The local distribution centre for Mukundpur, north west Delhi, is in a dingy office in the Jagiwan Ram Government hospital where the boxes of vaccine are kept in a freezer. At 6.30am last Sunday the vaccine was loaded into insulated containers with a packet of ice – it must be kept between four and eight degrees centigrade – and dispatched in one of 15 vehicles to supply 160 booths. We followed one of the routes down narrow streets thick with mud after heavy rain, stepping carefully – in the absence of toilets, the roadway must serve. Feral dogs picked over piles of rubbish, waterbuffalo lolled in a weed-covered swamp nuzzling bags of waste, while a pair of drowned goats floated nearby, their bellies already swollen.

We found the first booth on an empty lot sandwiched between ramshackle breezeblock dwellings – four tables and a few chairs under an imposing red and yellow awning festooned with posters proclaiming in English and Hindi: "End polio now".

It was already mobbed with children attracted by two westerners, UK rotary club members from a group of 50 visiting the programme (at their own expense) to see how their donations were being spent – £30m raised since 1985 and counting. They had also come to provide moral support to Indian colleagues whose passion for the cause might be waning after a decade and a half of continuous effort. Their yellow polo shirts and foreign appearance were as big a draw as the plastic balls Rotary provided for each child as a reward.

Your reporter was asked to volunteer and donning the Rotary colours, a yellow and red waistcoat, I held the vial of pink vaccine, lifted straight from the ice bucket, above the head of 17-month-old Angel as her father, Raju Chaurasia, 32, struggled to hold her still.

I shook a couple of drops into the nozzle and squeezed. Angel scowled, licked her lips and grimaced (the vaccine has a bitter taste). One down, only 171,999,999 to go.

How did Raju know about the vaccination day? He had seen it on TV. Why had he come? "She is my daughter, and polio is deadly and I didn't want her to suffer." Angel had been several times before, he said. In high risk areas such as this the NIDs are followed by local immunisation days, as many as 10 times a year. Maintaining the momentum of the campaign is crucial to success – a country is only declared polio free three years after its last case which will fall in February 2014 in India's case.

Chris Yates, who has been bringing groups of UK Rotarians to participate in the NIDs for almost a decade, described how in Uttar Pradesh, a polio hotspot, a resurgence of the disease in 2007-8 was only curbed when Muslim religious leaders were persuaded to join a committee to promote the vaccine locally.

On a visit to Pakistan he was warned that western volunteers would not be welcome – their presence likely to fuel rumours of a Western plot against the Muslim community.

While India prays polio will not return, for some the vaccine has come too late. The disease robs those afflicted of hope of an independent life – and their families too.

At St Stephen's Hospital in the north of the city, Dr Matthew Varghese runs the only ward dedicated to polio sufferers in all of India, where he attempts to restore independence even to those worst affected, who may have been crippled for decades.

He showed a picture of a young boy whose trunk was so grossly twisted he could sit up only by supporting himself on his hands. His father's wish was that his son should go to school. But as long as the boy needed his hands to support himself, he could not hold a pencil.

"My dream is to make sure this ward remains empty," Dr Varghese said.

The virus: a childhood scourge

Until the 1950s polio outbreaks occurred regularly across the world, terrifying parents and causing death and disability to thousands of children.

The polio virus infects nerve cells, destroying muscle function and eliminating tendon reflexes, especially in the legs, leaving the victim severely paralysed. In the worst cases it spreads into the brain stem, destroying the nerve cells that control breathing and swallowing. Survival then depends on artificial ventilation – thousands were treated in iron lungs – and tube feeding until the acute phase of the illness is past.

It is an intestinal virus that penetrates the lining of the gut and becomes lodged in the lymph nodes. There it causes fevers and stomach upsets, and passes back into the faeces. It can survive for up to 60 days outside the body, and in the absence of good hygiene and sanitation it can contaminate drinking water.

Jeremy Laurance

The vaccine: a miracle cure

Albert Sabin argued that his oral polio vaccine, launched in 1960, could be used to eliminate the disease. Coming five years after Jonas Salk’s vaccine (made from killed virus and injected), it had two advantages: it was easy to administer and, as a live virus, produced a mild contagious illness that spread immunity.

A trial in the 1950s in Toluca, Mexico, a town with a 100,000 population in which polio had broken out, proved its potential. In four days Sabin’s team vaccinated 26,000 children and in weeks polio disappeared from Toluca.

The oral vaccine provides “mucosal” immunity in the gut. It prevents the virus – transmitted when children put dirty fingers in mouths – penetrating the gut wall multiplying and causing disease. But this immunity is limited, hence the need for repeated doses.

In 1995 India used a trivalent vaccine against three types of the virus. Type 2 was eradicated in 1999, but not Type 3 and Type 1. Single vaccines were introduced in 2005 for each type and alternated each year, but Type 3 spiked in 2007-8. In 2010 a bivalent vaccine was introduced –and within a year, India had recorded its last polio case.

Jeremy Laurance