Effectiveness of the 23-valent pneumococcal polysaccharide vaccine against community-acquired pneumonia in older individuals after the introduction of childhood 13-valent pneumococcal conjugate vaccine: A multicenter hospital-based case-control study in Japan

Background: In the era of childhood pneumococcal conjugate vaccine (PCV) immunization, especially 13-valent pneumococcal conjugate vaccine (PCV13) immunization, serotype replacement of Streptococcus pneumoniae and herd immunity in adults have been reported worldwide. Therefore, continuous evalua-tion of the effectiveness of the pneumococcal vaccine in adults is crucial because vaccine effectiveness may change owing to these factors. The purpose of this study was to evaluate the effectiveness of the 23-valent pneumococcal polysaccharide vaccine (PPSV23) against all-cause pneumonia and pneumococ-cal pneumonia in older individuals with community-acquired pneumonia (CAP) after the introduction of childhood PCV13 in Japan, a topic that has remained largely unexplored.Methods: We evaluated pneumococcal vaccine effectiveness in this multicenter, matched case-control study conducted in hospitals and clinics. Cases included patients (aged >= 65 years) newly diagnosed with CAP between October 2016 and September 2019. A maximum of five non-pneumonia control patients matched for sex, school grade, date of outpatient visit, and medical institution were selected for each case. Conditional logistic regression models were used to calculate the odds ratios (ORs) and 95% confidence intervals (CIs) of pneumococcal vaccines for the occurrence of all-cause CAP and pneumococcal CAP.Results: The analysis included 740 individuals (142 patients and 598 controls). The median age of partici-pants was 75 years (men: 54%). The adjusted OR for pneumococcal vaccination against all-cause CAP was 1.31 (95% CI: 0.84-2.06), while that for PPSV23 vaccination in the previous 5 years was 1.33 (95% CI: 0.85-2.09). The adjusted OR for PPSV23 vaccination in the previous 5 years against pneumococcal CAP was 0.93 (95% CI: 0.35-2.50).Conclusions: This study was unable to demonstrate the effectiveness of PPSV23 against all-cause and pneu-mococcal pneumonia after the introduction of childhood PCV13 in Japan. Nonetheless, additional studies are needed to validate these results.(c) 2022 The Author(s). Published by Elsevier Ltd. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).