The effect of age and vaccination with a pneumococcal conjugate vaccine on the density of pneumococcal nasopharyngeal carriage
This study evaluated the impact of age and pneumococcal vaccination on density of pneumococcal nasopharyngeal carriage working with a cluster-randomized trial conducted in rural Gambia involving 21 villages.
This study evaluated the impact of age and pneumococcal vaccination on density of pneumococcal nasopharyngeal carriage working with a cluster-randomized trial conducted in rural Gambia involving 21 villages. Eleven villages were the vaccine group, where all residents received 7-valent-pneumococcal-conjugate-vaccine (PCV-7) while participants in the other 10 villages were the control group. Cross-sectional surveys (CSS) were conducted to collect nasopharyngeal swabs before-vaccination (baseline CSS) and 4, 12 and 22 months after-vaccination. Pneumococcal density was defined using a semi-quantitative classification (range 1-4) among colonized individuals. An age trend analysis of density was conducted utilising data from the baseline CSS. Mean pneumococcal density was compared in CSSs conducted before- and after-vaccination.
Results showed that mean bacterial density among colonized individuals in the baseline CSS was the same for both vaccine type (VT) and non-vaccine type (NVT) pneumococci which decreased with age for both.
While a decrease in density of VT carriage following vaccination was noted in individuals older than 5 years and in younger individuals in the vaccinated villages. Similar decreases in density were observed with NVT within vaccinated and control villages while no significant differences were found between vaccinated and control villages in the post-vaccination comparisons for either VT or NVT. Concluding that the high density of carriage among young subjects might partly explain why children are more efficient than adults in pneumococcal transmission and that pneumococcal vaccination appeared to lower density of carriage in a time trends analysis.
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