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Here is an example of how data for an infectious yet vaccine-preventable disease, pertussis, was summarized based on ages of disease incidence as well as recommended ages for vaccination. Of the 158 cases of pertussis reported to our surveillance system in 2001, the greatest proportion occurred among children < 6 months of age. Notice that during the first two years of life the age ranges span 6-month intervals while three-to-five-year spans were used to characterize cases occurring during the pre- and early elementary school years. Pre-adolescents, adolescents, and adults are grouped together in the last age group. The age categories spanned shorter durations (i.e., are narrow) for very young children where we know pertussis disease burden is high, and are large (i.e., broad) for older children and individuals > 10 years of age where disease burden is low.

The age categories in this example were also established to reflect the age ranges recommended for receipt of vaccination according to the Recommended Childhood Immunization Schedule used in the United States. Summarizing case data in this fashion allowed us to examine disease occurrence among children too young to be vaccinated versus those eligible to and who should have been vaccinated but were not. In this example, the cases of pertussis occurring among children < 6 months of age could not have been prevented through vaccination because these children were too young to have completed the recommended primary series of three vaccinations needed for baseline protection against pertussis. Conversely, at least some of the cases which occurred in children > 6 months of age could have been prevented because these children should already have received the recommended three doses of vaccine. Because cases of disease occurred among individuals > 10 years of age, this finding suggested that a waning of immunity, even among those who had already received all recommended doses of vaccine, was occurring. By summarizing our surveillance data in this way, we understood what additional information about cases needed to be obtained, and the type of public health action that needed to be taken. More specifically, we investigated the vaccination status of cases 7-23 months of age, identified the missed opportunities to vaccinate them, and changed our vaccination program to fill this pocket of need. By looking at the vaccination dates for cases > 10 years of age, we realized there might be a need for a booster dose of pertussis-containing vaccine, and thus, a need to change our vaccination policy such that a dose of pertussis-containing vaccine is recommend for older children, adolescents, and adults.

 
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