Interannual variation of the incidence of Haemophilus influenzae type b meningitis

We conducted a population-based retrospective cohort study to define the annual age-specific incidence of Haemophilus influenzae type b meningitis for birth to 5-year-old residents of King County, Washington, from January 1977 through December 1986. We found naturally occurring wide interannual variations in incidence. The standard deviations of the age-specific incidence during the eight years before the introduction of H influenzae vaccine varied from 26% to 115% of the mean. If short-term changes in incidence were used to assess the efficacy of an H influenzae vaccine (which is ( JAMA . 1989;261:1924-1929)