 This is a randomized cross-sectional study of the Swedish population. Blood samples will be collected from a subpopulation in order to estimate the age specific sero-prevalence of the Swedish population for diseases included in the National Immunization Program NIP, and to affirm the populations protection against polio. To be able to recommend complementary immunizations to immigrated children, a sub study focusing on foreign born teenagers will also be done and compared to children of the same age born in Sweden. 