Vaccine coverage estimation using a computerized vaccination registry with potential underreporting and a seroprevalence study.

OBJECTIVE: To develop a method to estimate vaccination coverage using both a computerized vaccine registry with an unknown underreporting rate and a seroprevalence study. A real example of a meningococcal C conjugate vaccine (MCCV) coverage estimation is studied to illustrate the proposed methodology. METHODS: We reviewed the Vaccine Information System of Valencia (Sistema de Información Vacunal, SIV) for the MCCV status of 1430 subjects aged 3-29 years as part of a seroprevalence study. When MCCV was not registered in SIV, subjects were classified into three groups (MCCV non-registered, no vaccination records and missing information) depending on the registry of other vaccines. A Bayesian model was developed to ascertain the percentage of MCCV-vaccinated subjects based on the meningococcal C seroprotection levels from the seroprevalence study. RESULTS: The seroprotection levels in subjects with no MCCV registered in SIV (358) were similar to those in subjects with MCCV registered (1072). This indicated a large proportion of vaccinated subjects with no MCCV registered. The estimated vaccine coverage was over 80% in all age groups, except >22 years, where it was 67.6% (95% CI: [54.0-80.4]), which corresponded to those aged over 13 years at the time of the catch-up campaign. An underreporting rate of 23.5-73.4%, depending on the age group, was estimated in those vaccinated in the 2002 catch-up campaign. CONCLUSION: The Bayesian model allowed for a more realistic estimation of MCCV uptake. In this example, we quantified the underreporting of a vaccine registry, especially occurring during a catch-up campaign that occurred at the establishment of the registry.