Consists of all people born within a given period of time, such as a calendar year.
National Immunization Surveys–Child (NIS–Child)
Collects data to estimate vaccination coverage among U.S. children aged 19–35 months by survey year for each year since 1994. In 2018, NIS changed the methodology and began reporting vaccination estimates by birth cohort. Each birth cohort is derived from survey data from the preceding 3 survey years.