Nasopharyngeal carriage of Streptococcus pneumoniae serotypes among children in The Republic of Khakassia, Russia

Abstract

Background: Nasopharyngeal (NP) colonization by Streptococcus pneumoniae (SP) precedes development of pneumococcal disease. We investigated the effect of pneumococcal conjugate vaccine (PCV) on the diversity and density of pneumococcal carriage in children after the introduction of PCV13 at the national level.

Methods: Nasopharyngeal swabs were collected from children <6 years-old (n=372) in 2019 with data about vaccination, five years post-PCV13-introduction. Specimens were cultured for pneumococci; Streptococcus pneumoniae were serotyped by Quellung reaction using commercial antisera (Statens Serum Institut).

Results: Overall SP colonization rate was 54,8% (204/372). Among  66,9% (249/372) PCV vaccinated-children, SP positivity was 51,8% (129/249) and vaccine serotype were 15.5% (20/129). Among 33,1% (123/372) non-PCV vaccinated-children, 61% (75/123) had NP colonization positive and PCV-13 serotypes were 14,7% (11/75). In total 28 serotypes were discovered. Five (2,5%) isolates were non-typeable. Serotypes 19F (n=13; 6,4%) and 3 (n=9; 4,4%) were the most common vaccine serotypes. Among non-PCV13 types, serotypes 11A (n=34; 16,7%), 15A (n=24; 11,8%), 15B/C (n=18; 8,8%), 23B (n=15; 7,4%) and 23A (n=10; 4,9%) were the most prevalent.

Conclusions: Our data suggests that Streptococcus pneumoniae colonization rate and serotype isolates were similar in vaccinated and unvaccinated children. Non-PCV13 serotypes increased in prevalence in the post-PCV period. Continued surveillance of serotypes is imperative to evaluate vaccine effectiveness and identify emergent replacement serotypes to inform future vaccine development.