Seroprevalence of antibodies against serogroup C meningococci in the region of Valencia, Spain: Impact of meningococcal C conjugate vaccination

Abstract Background and aims Meningococcal C conjugate (MCC) vaccination programs provide direct and indirect protection against meningococcal disease. However, a decrease in the antibodies could affect herd immunity. We conducted a seroprevalence study to assess the immunity in subjects 8–12 years after different MCCV vaccination programs were launched and evaluated the impact of vaccination on seroprotection. Methods Seroepidemiological study conducted from October 2010 to April 2012 in the region of Valencia, Spain. Sample size was not proportional to the population but to the expected seroprotection by age group. Sera from subjects that were ≥ 3 years old were tested using a standardized complement-mediated serum bactericidal antibodies (SBA) assay. Age-stratified proportions of subjects with SBA titers ≥ 8 were considered seroprotected and evaluated. A multivariate logistic regression model was performed to evaluate the impact of vaccination on the seroprotection. Results Serum samples from 1880 subjects were collected. In total, 523 (27.8%) of the 1880 subjects and 446 (31.2%) of the 1430 subjects < 30 years (targeted to any vaccination campaign) showed protective SBA titers. The highest percentage of seroprotected subjects (67.8%, 95%CI 56.9–77.4) was observed in those that were vaccinated in a catch-up campaign at 10–13 years of age (20–21 years old at the time of blood sampling). Those scheduled for immunization in infancy at 2, 4 and 6 months of age (7–8 years at blood sample) represented the lowest (7.1%, 95% CI 3.3–13.1) number of seroprotected subjects. Having received one vaccine dose after 12 months of age was associated with increased seroprotection. The present study revealed a positive correlation between the increasing age at vaccination and longer duration of seroprotection. Conclusion Only one in three subjects who were vaccinated with MCC vaccine was seroprotected after 8–12 years. These findings emphasize that seroprevalence studies are essential to identify susceptible cohorts and to inform vaccine policy.