"The second important feature evident from the review of age-specific attack rates is that school children invariably have the highest attack rates during both pandemic and interpandemic periods. Epidemiologic studies during pandemics have demonstrated that children are important for spread of virus in the community. Observations made during the two major pandemics of this century reinforce the thesis that school children are important in the spread of influenza. Even though the populations were universally susceptible to the new influenza viruses that emerged in 1918 and 1957, and even though both viruses had seeded the population in the preceding spring and summer, the first major wave did not occur until schools were in session. Peak activity of both pandemics occurred in late October after school had been in session for 6-8 weeks. For interpandemic periods, observations in Houston have demonstrated that schoolchildren predominate among persons presenting for health care during the early stage of influenza epidemics. The age distribution of culture-positive patients changes during the course of the epidemic, with a shift to preschool children and adults during the latter part of the epidemic (table 4). School absenteeism occurs in the first part of the epidemic and employee absenteeism occurs during the later part. Hospitalizations of persons aged 65 years and older tend to occur during the last half of the epidemic, and pneumonia-influenza deaths are lagged at least 2 weeks after the peak of community morbidity. All of these observations support the thesis that school children are important disseminators of the virus in the community for both pandemic and interpandemic influenza. A series of family studies also have demonstrated that children are the main introducers of influenza into the household, and have found that immunization of school children would be effective for epidemic control."