They said India would be the last country to stop polio. The feat was near impossible: to find and immunize more than 170 million children behind every door of every dwelling in this vast sub-continent; to reach the millions who didn’t even exist on a map - brick kiln workers, construction workers, slum dwellers, nomads; to provide two drops of oral polio vaccine to protect India’s children from the most intense transmission of wild poliovirus on the planet, in one of the most heavily, densely populated countries on earth. In each national polio immunization campaign in India, more than 170 million children are vaccinated by more than two million vaccinators.