The impact of higher-valency pneumococcal conjugate vaccine use on pediatric parapneumonic pleural effusion/empyema in Belgium.

<bold>Purpose</bold>: Parapneumonic pleural effusion and empyema (PPE/PE) are severe complications of community-acquired pneumonia, with <italic>Streptococcus pneumoniae</italic> being the most frequent pathogen in children. Widespread pneumococcal immunization for infants aims to reduce invasive pneumococcal infections, but vaccine recommendations changed repeatedly. We investigated the pneumococcal etiology and serotypes in PPE/PE in a tertiary care center in Belgium, over a period of 8 years with changing pneumococcal conjugate vaccines (PCV) use, namely PCV7, PCV10 and PCV13. <bold>Methods:</bold> Children < 18 years of age admitted to the Pediatric Department of University Hospitals Leuven between December 2012 and March 2020, undergoing a pleural tap for PPE/PE, were included. All bacteria detected in blood or pleural fluid (by culture/PCR) were included, with serotyping for <italic>S. pneumoniae.</italic> <bold>Results:</bold> 50 children were included with a median age of 3.4 years (IQR 2-5). A bacterial pathogen was identified in 35/50. These were mostly (28/35) <italic>S. pneumoniae</italic>, from which 12/28 serotype 3 and 10/28 serotype 1. <italic>Streptococcus pyogenes</italic> caused 7/35 infections. From 42/50 children with available immunization data, twelve completed the PCV13 immunization. Six out of seven cases with PCV13 failure had a serotype 3 infection. There were no cases of PCV7 or PCV10 failure, and no serotype 19A infections. <bold>Conclusion:</bold> <italic>S. pneumoniae</italic> remains the major pathogen in PPE/PE in our cohort, but the importance of <italic>S. pyogenes</italic> cannot be neglected. PCV13 provided sufficient protection against serotype 1 and 19A complicated pneumonia, but failed for serotype 3.