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.
