In the past 10 years worldwide (as of September 2007), more than 10 billion doses of oral polio vaccine have been administered to more than 2 billion children.
Travellers from Pakistan should have a full course of vaccination against polio before leaving Pakistan, with a minimum one dose of OPV before departure.
Live vaccines, such as oral poliovirus vaccine; yellow fever vaccine; and measles, mumps and rubella vaccines, do not contain thiomersal, because it would kill the immunizing component.