Poliomyelitis is an acute viral infection of the nervous system. Worldwide more than half of infections are in children under five. One in two hundred infections leads to permanent paralysis, usually in the legs. In 5-10% of these cases the victims die when the breathing muscles are paralysed. As it is the most harmful diesease the parents of 24,000 children in northern Pakistan refused to allow health workers to administer polio vaccinations last month, mostly due to rumours that the harmless vaccine was an American plot to sterilise innocent Muslim children. But the tail has a deadly sting. Even though only 24,000 children missed the vaccine, the WHO officials said failure to vaccinate in small pockets of the country gave the virus a fresh toehold to spread.-BISMA ABBASI, Karachi, via e-mail, October 4.