Abstract
Between 1955 and 1963, an estimated number of 150 mill people in various parts of the world, including Norway, received poliomyelitis vaccine possibly contaminated with infectious simian virus 40 (SV40). Human studies have investigated the hypothesised association between SV40 and various cancers, but the results have so far been contradicting. The aim of the present study was to examine Norwegian cancer incidence data to assess a possible association between the incidence rate of lymphoproliferative disorders, and birth cohorts assumed to have been subjected to the vaccine. Between 1953 and 1997, the incidence rate of lymphoproliferative diseases increased about three-fold in both males and females. Age-period-cohort modelling showed that the cohort effect was more prominent than the period effect. Although the variations in incidence pattern to some extent fit with the trends as expected if a SV40 contaminated vaccine did play a causative role, crucial parts of the cohort pattern deviate from the expected trend. Thus, our data do not support the hypothesis of an association between the vaccine and lymphoproliferative diseases. A significant upward trend shift was observed for those who were born after 1932. These cohorts were in childhood and early adolescence during WWII, a period when the Norwegian population was exposed to an increased infectious load through a relatively large contingent of German soldiers, civilians, and prisoners of war. This finding extends the prevailing notion of an infectious etiology to the disease by suggesting that infectious exposure early in life is of particular importance in establishing the risk for lymphoproliferative diseases.