 One factor contributing to the continued circulation of polio immunization programs has been opposition in some countries.In the context of the United States invasion of Afghanistan and the subsequent 2003 invasion of Iraq, rumours arose in the Muslim world that immunization campaigns were using intentionally-contaminated vaccines to sterilize local Muslim populations or to infect them with HIV.In Nigeria these rumours fit in with a longstanding suspicion of modern biomedicine, which since its introduction during the era of colonialism has been viewed as a projection of the power of western nations.