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.