Background

Nasopharyngeal carriage of Streptococcus pneumoniae is extremely prevalent in The Gambia. We studied the effects of vaccination with pneumococcal conjugate vaccines on the carriage of individual serotypes and on antimicrobial resistance in vaccinated children and their younger siblings.

Methods

A longitudinal study of a subsample of children (n=2342) who participated in a randomized, placebo controlled trial of a 9-valent pneumococcal conjugate vaccines (PCV-9) in The Gambia, and a cross-sectional study of non-PCV-9-vaccinated younger siblings (n=675).

Results

Recipients of PCV-9 were less likely to carry vaccine serotypes 4, 6B, 9V, 14, 19F, and 23F but more likely to carry vaccine-associated 19A and 9 nonvaccine serotypes at approximately 6 months postvaccination (age, 12 months) than were controls (each P<0.05). At approximately 16 months postvaccination, carriage of vaccine-associated-serotype 6A was also significantly reduced (P<0.01) while 3 other nonvaccine serotypes were more prevalent in the PCV-9 recipients (each P<0.05). At 16 months, but not 6 months, postvaccination PCV-9 recipients had lower rate of carrying isolates resistant to tetracycline and trimethoprim-sulfamethoxazole (TMP-SMZ) than controls (risk ratio: 0.90 and 0.95, respectively; each P<0.05). There was no difference in patterns of carriage of pneumococci in younger siblings of PCV-9 or placebo recipients.

Conclusions

The effects of 9-valent pneumococcal conjugate vaccines on carriage of pneumococci persisted for at least 16 months postvaccination in Gambian children. Vaccination had no indirect effect on carriage in younger siblings and there was limited impact on antibiotic resistance.