Effectiveness of conjugate vaccine against Neisseria meningitidis serogroup C in children under two years

Abstract

To estimate direct effectiveness of conjugate vaccine against Neisseria meningitidis serogroup C (MCCV) in children under two years and to assess its direct and indirect impact in birth cohorts of children that have and do not have indication for vaccination. Methods: Direct vaccine effectiveness will be estimated in a population-based case-control study conducted in the city of São Paulo, southeastern Brazil. Cases will be matched with four controls by area of residence. The direct and indirect impact of MCCV will be assessed in a descriptive study. For the case-control study, cases are defined as children in birth cohorts that have indication for MCCV vaccination since 2010 when the vaccine was introduced in Brazil and who had group C meningococcal disease (MD) confirmed by culture or real-time polymerase chain reaction. Controls are defined as children in the same birth cohorts with no MD at the time of disease occurrence of the case. Immunization status will be verified in immunization records for cases and controls. Cases will be identified in MD surveillance records in the city of São Paulo between January 1, 2011 and December 31, 2013. The direct effectiveness of the vaccine will be calculated by the following formula: 1 - odds ratio (OR) of MCCV vaccination. A multiple regression analysis will be performed to estimate ORs and their related 95% confidence intervals (95% CI) using as dependent variable serogroup C MD, adjust for potential confounders. The likelihood ratio test will be performed to evaluate statistical significance of variables in the models. The direct and indirect impact of the vaccine will be assessed by estimating MD incidence by age on a monthly basis for a period between 36 months preceding the beginning of vaccination (September 2010) and 36 months from the beginning of vaccination. Relative risks (RR) of monthly incidences will be estimated taking the 12 months prior to the beginning of vaccination as reference. The chi-square test (X2) will be used for comparative analysis. Expected results: Our results will be analyzed and compared with international data and can provide insight to improve MD control strategies in Brazil. (AU)