Emergence of antibiotic-resistant pneumococcal serotypes causing invasive pneumococcal disease in children, Spain

Pneumococcal conjugate vaccines (PCVs) have significantly reduced disease burden caused by <i>Streptococcus pneumoniae</i>, a leading cause of childhood morbidity and mortality globally. The rise of non-vaccine serotypes is a frequent phenomenon after the use of these PCVs. This study is a national surveillance that includes all pneumococcal isolates causing invasive pneumococcal disease (IPD) (4,455 isolates) in the pediatric population to analyze the changes of strains with reduced susceptibility (IPD-RS) to different antibiotics (1,458 to penicillin/1,304 to erythromycin) and the impact of PCVs and COVID-19 pandemic on antibiotic resistance. Six periods are differentiated according to this decline: pre-PCV13, early PCV13, middle PCV13, late PCV13, COVID-19, and reopening. Between 2009 and 2023, overall IPD cases in Spain decreased by over 60% in children aged 1-4 years and by approximately 50% in infants under 1 year of age. Nevertheless, an increase in IPD-RS caused by non-PCV13 serotypes was observed, with serotype 24F being the most prevalent, which is not included in the currently licensed PCVs. The introduction of PCV13 showed a substantial impact on reducing IPD in children. The COVID-19 pandemic led to a temporary decline in the burden of disease caused by resistant strains in 2020 due to non-pharmacological measures followed by a subsequent recovery.