Evaluation of the association of pneumococcal conjugate vaccine immunization and density of nasopharyngeal bacterial colonization using a multiplex quantitative polymerase chain reaction assay.

BACKGROUND: Nasopharyngeal bacterial colonization is a pre-requisite for developing bacterial mucosal and invasive disease. Pneumococcal conjugate vaccine (PCV) immunization of children reduces their risk of colonization by vaccine-serotypes, which could affect the biome of the nasopharynx in relation to colonization by other bacteria. This study evaluated the association of PCV immunization on the prevalence density of nasopharyngeal colonization by common, potentially pathogenic bacteria.

METHODS: A multiplex qPCR assay was used to evaluate bacterial nasopharyngeal colonization by 7-valent PCV (PCV7) serotypes, non-vaccine serotypes (NVT), Haemophilus influenzae, Staphylococcus aureus, Moraxella catarrhalis, and Neisseria meningitidis in PCV7-vaccinated and PCV-unvaccinated African children at two time points.

RESULTS: PCV7 vaccination was associated with a higher prevalence of NVT and H. influenzae at 9 and 16 months, respectively. While the prevalence of S. aureus was higher in PCV7-vaccinated children at 9 months, no difference was found at 16 months. The density of PCV7 serotypes (3.8 vs. 3.4 log10 ; p = 0.048), NVT (3.6 vs. 3.1 log10 ; p = 0.018), H. influenzae (4.34 vs. 3.86 log10 ; p = 0.008), M. catarrhalis (3.52 vs. 2.98 log10 ; p < 0.001) and S. aureus (4.02 vs. 3.06 log10 ; p = 0.02) was higher among PCV-vaccinated compared to PCV-unvaccinated children at 9 months, although, this difference diminished at 16 months of age.

CONCLUSION: The reduction in PCV7-serotype colonization impacted on colonization prevalence and density of other bacterial species of the nasopharynx. The clinical relevance of this needs further exploration in relation to mucosal and invasive disease outcomes, as well as for higher valency PCV vaccines.