In 2007 and 2008, the Kosi River area opened a new frontline in the last battle against polio in India. At the time, more than 70 percent of all polio in the state was concentrated in just 16 percent of its area. In these 72 blocks out of 450, imported poliovirus would take root and circulate rather than causing isolated cases. More than half of those blocks were dotted along the Kosi floodplains - home to 500,000 of children living without roads, electricity or government institutions.