http://www.eurosurveillance.org/ViewArticle.aspx?ArticleId=2099
Seroepidemiological surveys have shown that more than 97% of Norwegians born before the introduction of measles immunisation in 1969 had contracted measles. This confirms the assumption that almost all children in Norway contracted measles before the vaccine was introduced.

http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1646302/pdf/amjph00283-0041.pdf

In the absence of a vaccination program, members of a birth cohort become infected at different ages based on the epidemiologic characteristics of the disease. Age-specific infection rates can be determined either from the seropreva- lence of antibodies to the agent by age, or from historical surveys which determine the age at which infection occurred.For example, in the case of measles we know that prior to the initiation of vaccination programs 95 per cent of individuals in an unvaccinated population have evidence of infection by age 30