Molecular epidemiology of pneumococcal carriage in children from Seville, following implementation of the PCV13 immunization program in Andalusia, Spain

The 13-valent pneumococcal conjugate vaccine (PCV13) universal vaccination programme was introduced in December 2016 in Andalusia. A cross-sectional study was conducted on the molecular epidemiology of pneumococcal nasopharyngeal colonization. A total of 397 healthy children were recruited from primary healthcare centres in Seville for the periods 1/4/2018 to 28/2/2020 and 1/11/2021 to 28/2/2022 (PCV13 period). Data from a previous carriage study conducted among healthy and sick children from 1/01/2006 to 30/06/2008 (PCV7 period), were used for comparison of serotype/genotype distributions and antibiotic resistance rates. Overall, 76 (19%) children were colonized with S. pneumoniae during the PCV13 period and there were information available from 154 isolates collected during the PCV7 period. Colonization with PCV13 serotypes declined significantly in the PCV13 period compared with historical controls (11% vs 38%, p = 0.0001), being serotypes 19F (8%), 3 (1%) and 6B (1%) the only circulating vaccine types. Serotypes 15B/C and 11A were the most frequently identified non-PCV13 serotypes during the PCV13 period (14% and 11%, respectively); the later one increased significantly between time periods (p = 0.04). Serotype 11A was exclusively associated in the PCV13 period with ampicillin-resistant variants of the Spain9V-ST156 clone (ST6521 and genetically related ST14698), not detected in the preceding period. There was a residual circulation of vaccine types following PCV13 introduction, apart from serotype 19F. Serotype 11A increased between PCV13 and PCV7 periods due to emergence and clonal expansion of ampicillin-resistant genotype ST6521. El programa de vacunación universal con la vacuna antineumocócica conjugada 13-valente (VNC13) se implantó en Andalucía en diciembre de 2016. Estudio transversal de colonización nasofaríngea por Streptococcus pneumoniae. Se reclutaron 397 niños sanos en centros de atención primaria de Sevilla durante los periodos 1/4/2018 al 28/2/2020 y 1/11/2021 al 28/2/2022 (periodo VNC13). Se utilizó una colección histórica de un estudio de colonización desarrollado en niños sanos y con infección respiratoria superior entre el 1/01/2006 y 30/06/2008 (período VNC7) para comparar las distribuciones de serotipos/genotipos y las tasas de resistencias antibióticas. Un total de 76 (19%) niños estaban colonizados con S. pneumoniae en el período VNC13 y se dispuso de 154 aislamientos del período VNC7. La colonización por serotipos incluidos en