Association between introduction of 13-valent pneumococcal conjugate vaccine and burden of hospitalized adult pneumococcal disease in South Korea – a population-based retrospective database study

Abstract Background Information on the burden of pneumococcal disease and its association with vaccination in South Korea remains limited. This study aims to examine the incidence rate, case fatality rate, healthcare resource utilization and costs of pneumococcal disease in adults before and after the introduction of 13-valent pneumococcal conjugate vaccine (PCV13) into South Korea’s childhood immunization program (CIP) in 2014. Methods Episodes of eligible adults aged at least 18 years hospitalized with invasive pneumococcal disease or pneumonia between 1 January 2010 and 31 December 2019 were extracted from South Korea’s National Health Information Database. The Korean version of the International Classification of Diseases codes were used for case identification. Study findings were compared between pre-CIP (2010–2013) and post-CIP (2015–2019) periods. Changes in the level and slope change of incidence rates in the post-CIP period were assessed with interrupted time series analyses and reported using incidence rate ratio (IRR). Healthcare resource utilization components consisted of length of hospitalization, and number of inpatient, outpatient and emergency department visits. Direct costs were calculated. Results There were a total of 1,682 invasive pneumococcal disease episodes and 8,635 pneumonia episodes included in this study. Overall incidence rates for invasive pneumococcal disease and pneumonia were 0.4 and 2.1 episodes per 100,000 person-years, respectively. For invasive pneumococcal disease, there were no significant changes in the level of incidence rate (IRR = 1.26; 95% confidence interval [CI]: [0.99, 1.59]) and slope of incidence rate (IRR = 0.97; 95% CI: [0.93, 1.01]) in the post-CIP period. For pneumonia, level of incidence rate was significantly higher in the post-CIP period than in the pre-CIP period (IRR = 1.92; 95% CI: [1.51, 2.42]), but no difference in slopes were observed between the two time periods (IRR = 1.02; 95% CI: [1.00, 1.04]). Case fatality rate was 14.9% for invasive pneumococcal disease and 3.0% for pneumonia. The average total costs per pneumonia episode was higher in the post-CIP period (4.1 vs. 3.1 million Korean Won). Disease burden was generally higher in patients ≥ 65 years. Conclusions Incidence of invasive pneumococcal disease remained stable while incidence and economic burden of pneumonia in adults had increased after PCV13 introduction into South Korea’s CIP. Use of PCV13 and factors such as increased surveillance may explain the observed results.