Effect of the 13-valent pneumococcal conjugate vaccine on pneumococcal carriage in rural Gambia 10 years after its introduction: A population-based cross-sectional study

<h4>Background</h4>Sub-Saharan Africa has a high burden of pneumococcal diseases. Pneumococcal carriage precedes invasive disease and transmission. The introduction of pneumococcal conjugate vaccines (PCVs) has significantly reduced global vaccine-type (VT) pneumococcal disease, but data on PCVs' long-term impact on VT serotypes in Africa are limited. We aimed to evaluate PCV13's long-term effect on pneumococcal carriage in rural Gambia.<h4>Methods</h4>From January to November 2022, we conducted a population-based, cross-sectional pneumococcal carriage survey in Central and Upper River Regions of The Gambia. We collected data on demographic characteristics, clinical history, risk factors, and PCV status. Nasopharyngeal swabs were taken from randomly selected household members of all ages. Streptococcus pneumoniae was isolated and serotyped using standard methods. We measured the prevalence of pneumococcal carriage by specific age groups, PCV13 vaccination status, and the proportions of different pneumococcal outcomes among carriers. We performed multivariable logistic regression to examine factors associated with VT carriage.<h4>Results</h4>Overall, 4087 participants were enrolled; the prevalence of pneumococcal carriage was 32.1% (95% CI: 29.34% - 35.03%). The estimated prevalence of PCV13 VT carriage was 6.4% (95% CI: 5.48% - 7.47%). Children aged 5-9 years had the highest VT carriage prevalence at 13.6% (95% CI: 10.34% - 17.56%). Among fully PCV-vaccinated children under 10, the odds of VT carriage in 5-9-year-olds were 1.60 times higher than in infants aged 0-11 months [AOR = 1.60, 95% CI:1.06-2.41]. The prevalence of VT carriage was similar among fully PCV-vaccinated and unvaccinated children under 10 years of age. Serotypes 19F, 3 and 6A were the most abundant VTs; 19F and 3 were the most prevalent among <5 and 5-14-year-old children, respectively.<h4>Conclusions</h4>Ten years after the introduction of PCV13 in the Gambia, residual VT carriage persists, particularly in age groups in whom direct protection from immunization in infancy has waned. A booster dose or catch-up vaccinations could aid control of VT circulation.