The polio virus has been found in the sewers of Cairo, and it appears to have come from Pakistan, the World Health Organization said Wednesday. Egypt has not had a case of polio since 2004. A vaccination drive is being planned for Feb. 25, and health workers are canvassing the neighborhoods where the sewage samples were taken, looking for children or adults who may have recently been paralyzed, said Sona Bari, a spokeswoman for the W.H.O. Pakistan has said it will post teams at its international airports vaccinating all outward-bound passengers under age 5. Last month, at least nine Pakistani volunteers in an internationally supported polio vaccination drive were killed by militants across Pakistan in a campaign of intimidation that has hurt efforts to eradicate the disease there. Pakistan is one of the last three countries, with Afghanistan and Nigeria, with indigenous polio.