Vaccine 33 (2015) 2183–2188 Contents lists available at ScienceDirect Vaccine j our na l ho me page: www.elsevier.com/locate/vaccine Vaccine coverage estimation using a computerized vaccination registry with potential underreporting and a seroprevalence study Lina Pérez Breva a , Javier Díez Domingo a,∗ , Miguel Ángel Martínez Beneito b , Joan Puig Barberà a a Vaccine Research, Foundation for the Promotion of Health and Biomedical Research in the Valencian Region FISABIO – Public Health, Avenida Catalu˜ na 21, CP 46020 Valencia, Spain b Health inequalities, Foundation for the Promotion of Health and Biomedical Research in the Valencian Region FISABIO – Public Health, Avenida Catalu˜ na 21, CP 46020 Valencia, Spain a r t i c l e i n f o Article history: Received 7 November 2014 Received in revised form 26 January 2015 Accepted 17 February 2015 Available online 5 March 2015 Keywords: Meningococcal C conjugate vaccine Vaccination coverage Electronic immunization registries Seroprevalence studies Validation studies Underreporting Bayesian model a b s t r a c t Objective: To develop a method to estimate vaccination coverage using both a computerized vaccine reg- istry 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 vaccina- tion 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. © 2015 Published by Elsevier Ltd. 1. Introduction Accurate classification of subjects’ immunization status is essen- tial for clinical care, administration and evaluation of immunization programs as well as vaccine program research. Immunization pro- gram administrators and researchers need to institute measures to identify and reduce the misclassification of immunization sta- tus so that registries can play an effective role in the control of vaccine-preventable diseases [1]. The assessment of accurate vaccine coverage is important to understand the impact of a vacci- nation program and to develop new strategies. ∗ Corresponding author. Tel.: +34 961925937. E-mail address: diez jav@gva.es (J.D. Domingo). The recent introduction of vaccines in adolescent and young adults, especially if given in mass catch-up campaigns, may result in a lower registration rate for the vaccines administered. This may be the case with meningococcal C conjugate vaccine (MCCV). This vaccine has proved to be extremely effective, not only for its direct effect but also for its indirect effect due to herd immunity. Countries with high vaccination coverage and extensive catch-up programs have shown that the vaccine prevents disease even in the unvacci- nated [2,3]. In Spain, the program decreased the burden of disease, but its incidence in subjects older enough to be excluded from the catch-up program has remained stable for a long period of time. One hypothesis explaining this is that the catch-up program was not as exhaustive as in the UK or the Netherlands [2,4]. In the Valen- cian Region of Spain, in 2000, MCCV was scheduled at 2, 4, and 6 months of age, with an active catch-up recommended up to 6 years of age [5], and in 2002, a passive catch-up was expanded up to 19 http://dx.doi.org/10.1016/j.vaccine.2015.02.048 0264-410X/© 2015 Published by Elsevier Ltd.