Use of surveillance data to estimate the effectiveness of the 7-valent conjugate pneumococcal vaccine in children less than 5 years of age over a 9 year period.

Abstract Background Case–control studies evaluating post-licensure effectiveness of conjugate vaccines can be laborious and costly. We applied an indirect cohort method to evaluate the effectiveness of seven-valent pneumococcal conjugate vaccine (PCV7) against invasive pneumococcal disease (IPD) and compared the results to the effectiveness measured using a standard case–control study conducted during the same time period. Methods IPD cases among children 2–59 months old were identified through the Active Bacterial Core surveillance system during 2001–2009. We used logistic regression to calculate the odds ratio of vaccination (versus no vaccination) among cases (PCV7-type IPD cases) and non-cases (non-PCV7-type IPD cases), controlling for the presence of underlying conditions. Vaccine effectiveness (VE) was calculated as one minus the adjusted odds ratio. Results Among 4225 IPD cases reported during 2001–2009, 2680 (63%) had serotype information and vaccine history. Effectiveness of ≥1 dose of PCV7 against PCV7-types was 88% (95% confidence interval (CI) 78–94%) among children with comorbid conditions and 97% (95% CI 92–98%) among healthy children. Among healthy children, VE was higher in 2001–2003 (97%, 95% CI 95–98%) compared to 2004–2009 (81%, 95% CI 64–90%). The annual estimates of VE in 2004–2009 showed great variability and wide confidence intervals due to the small number of PCV7-type cases. Conclusions An indirect cohort design using IPD surveillance data confirms the findings of the case–control study and, therefore, appears suitable for estimating PCV7effectiveness. This method would be most useful shortly after vaccine introduction, and less useful in a setting of very high vaccine coverage and fewer vaccine-type cases.