Impact of pneumococcal conjugate vaccines on S. pneumoniae carriage in infant and toddlers with acute otitis media in Morocco.

BACKGROUND: Streptococcus pneumoniae remains a major cause of pediatric infections despite pneumococcal conjugate vaccines (PCVs). In Morocco, the concurrent use of PCV10 and PCV13 offers a unique opportunity to evaluate their impact on nasopharyngeal carriage and serotype distribution. OBJECTIVE: To describe pneumococcal serotypes in the nasopharyngeal flora of young children with acute otitis media (AOM) in Casablanca and to compare serotype distribution according to vaccination status. METHODS: In this prospective, multicenter, cross-sectional study (2020-2024), children aged 6-36 months with AOM had a nasopharyngeal swab performed. Isolates were serotyped by Quellung reaction and PCR and classified as vaccine (VTs) or non-vaccine types (NVTs); Haemophilus influenzae isolates were serotyped by slide agglutination. RESULTS: Of 442 children, 172 pneumococci were recovered (carriage rate of 38.9%), representing 18 serotypes. PCV10 serotypes accounted for 49.4% and additional PCV13 serotypes for 21.5%; the main non-PCV13 serotypes were 11 A, 15B, and 10 A. Theoretical coverage reached 73.8% for PCV15 and 92.4% for PCV20. Among 136 isolates tested, two were fully penicillin-resistant (MIC >2 mg/L). Of 74H. influenzae isolates, 10.8% were serotype b and 20.3% serotype f; β-lactamase production was found in 10.8%, and a BLNAR phenotype in six isolates (8.1%). CONCLUSION: Persistent vaccine-type carriage alongside emerging non-vaccine serotypes indicates incomplete serotype replacement in Morocco. PCV13 provided broader coverage than PCV10, mainly through serotypes 19 A and 3. Most non-PCV13 serotypes were included in PCV20, supporting its potential integration into the national immunization program and continuous serotype surveillance.