Health workers in Pakistan are marking children’s fingers as having had a polio vaccination, when in reality parents have refused the vaccine after believing conspiracy theories that they are harmful, blasphemous, or a plot to sterilise Muslims. This is the biggest challenge - to eradicate the crippling virus in one of its last haunts. Deteriorating security along the border is making the situation worse, as militants cross from Afghanistan - the only other country where polio is still circulating. After two years free of polio Pakistan has two poliovirus cases. They were also paralysed, raising further concerns that there may still be hundreds of cases in the region. On average, only one in 200 infections leads to paralysis. Bill Gates, who invests billions in the polio fight, said ‘it would be tragic if the disease made a comeback because it would spread back across the world and eventually you have what you had before 1988 - hundreds of thousands of paralysed children.’