Variola minor in Bragança Paulista County, 1956. Distribution of onset of cases in the two schools including most school children with variola.

Class attendance during illness was confirmed for numerous pupils of two schools. Successive generations whose median cases were separated by an interval consistent with the "serial interval" of variola minor were clearly found in the epidemic curve for II of the 29 classes with cases from both schools. Twenty two other classes had no case at all.