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Polio is a devastating disease that still exists in some parts of the world, despite an unprecedented global health campaign to get rid of it. Children are particularly at risk and Indian-born Gautam Lewis was just one among many millions to contract the virus.

Raised in a Calcutta orphanage, his life might have remained one of grinding poverty - had he not been adopted at the age of seven and taken to live in privilege and comfort in Britain. Twenty three years on, Gautam leaves his London home and returns to the country of his birth.

India is one of just four countries in the world where polio remains endemic and Gautam travels back to take part in National Immunisation Day when, it is hoped, more than 75 million children will be vaccinated. So far it has cost $5 billion and involved 20 million vaccinators across the world. But all this money and effort could be wasted if the disease is not now erased forever.

As long as polio exists in one country, every country must keep vaccinating. The Gates Foundation has just promised $100 million of the $200 million needed to fund the final push towards global eradication. It is an international story of epic proportions that highlights the problems - and achievements - of an extraordinary global collaboration.

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About Al Jazeera - Witness

Rageh Omaar presents Witness, a half-hour daily documentary series which features short, specially commissioned or acquired films gathered from independent filmmakers.
 
Each documentary reveals the unknown lives of ordinary people, following their lives, telling their stories and portraying the challenges that confront them. Our witnesses are people in a situation or those who have observed them first hand.
 
The films cover conflict, belief, the past and the future and as well as bringing new stories to light they showcase the talents of a new breed of multi-skilled, frontline journalist. In the studio, Rageh will further explore the issues raised in the films, with expert guests on the subject matter and the filmmakers themselves.