Evaluation of the effectiveness of pneumococcal conjugate vaccine for children in Korea with high vaccine coverage using a propensity score matched national population cohort

Objectives: This study was performed to evaluate the vaccine effectiveness (VE) of protein conjugated pneumococcal vaccines (PCV) in children with regard to all-cause pneumonia (ACP), pneumococcal pneumonia (PP), invasive pneumococcal disease (IPD), and acute otitis media (AOM), in a country where the unvaccinated group is very small. Methods: Children born between 2013 and 2015 were identified in the national population registry for retrospective observation. Vaccination history from the National Immunization Program registry and medical records from the National Health Insurance System were linked together to set up a cohort. VE based on original and propensity score matched cohorts were estimated and compared. Results: A total of 990 224 children were included and 98% were vaccinated. The crude incidence of ACP, PP, and AOM for the original cohort was heavily skewed to the vaccinated group. Adjusting for age, sex, comorbidity, and healthcare utilization rate, the vaccine was found to be effective against PP (VE 60.15%, 95% confidence interval (CI) 21.21–79.85%) and AOM (VE 19.13%, 95% CI 13.42–24.46%). The propensity score matched cohort showed VE against ACP (5.95%, 95% CI 0.88–11.57%), PP (48.61%, 95% CI 23.60–65.43%), and AOM (33.21%, 95% CI 31.01–35.33%). Conclusions: The direct effect of the PCV program was confirmed for ACP, PP, and AOM. The propensity score matched cohort is a feasible solution for measuring and tracing nationwide VE in countries with a very high level of vaccine coverage.