2025/01/01 by I Osei · 1 voice
Medicine · Social Sciences · #Pneumonia and Respiratory Infections #Respiratory viral infections research #Vaccine Coverage and Hesitancy
paper · doi:10.17037/pubs.04678300
openalex publication_date 2025/01/01 · openalex created_date 2026/01/29 · openalex updated_date 2026/07/01
The Gambia introduced the pneumococcal conjugate vaccine (PCV7) into its routine Essential Program on Immunisation (EPI) using a three-dose schedule without a booster dose (i.e. a ‘3p + 0’ schedule) in August 2009, which was subsequently replaced with PCV13 in May 2011. Pneumococcal carriage is a necessary precursor for invasive pneumococcal disease (IPD) and the transmission of pneumococci. Despite the prolonged use of PCV in The Gambia and other African countries with high vaccine coverage, vaccine-type (VT) pneumococcal carriage persists. This residual VT carriage is concerning as it has the potential to sustain pneumococcal transmission and cause a continued disease burden in the population. In this thesis, I aimed to assess the roles of population age groups and social contact patterns in contributing to the persistent carriage of VT pneumococci in rural Gambia after a decade of PCV13 usage. Firstly, in 2022, I designed and conducted a nested population-based, cross-sectional social contact survey within a larger pneumococcal carriage survey in the Central and Upper River Regions of The Gambia. Those aged 5-9 years had the highest prevalence of VT carriage [13.6% (95% CI: 10.3% - 17.6%)], followed by those aged 0–11 months [10.5% (95% CI: 8.5% - 12.8%)], and those aged 24-59 months [10.4% (95% CI: 8.5% -12.6%)]. Among fully PCV-vaccinated children aged <10 years, the odds of VT pneumococcal carriage were 1.60 times higher for those aged 5-9 years compared to infants aged 0-11 months [Adjusted Odds Ratio (AOR) = 1.60, 95% CI = 1.06 – 2.41]. Among pneumococcal carriers, the proportion of VT carriage was significantly higher in the 5–14-year-old group, at 31.5% (95% CI: 26.4% - 37.2%) compared to those aged 0– 4 years with a proportion of 16.8% (95% CI: 14.6% - 19.2%). I found that social contact patterns were primarily driven by mixing within households. Most contacts were physical and mostly age-assortative; children aged 5-14 years had the highest mean number of physical contacts [11.3 (95% CI: 10.9 - 11.8)], followed by those aged 15–44 years [10.4 (95% CI: 9.9 - 10.8)]. Physical contact was associated with VT carriage [1.22 (95% CI: 1.00 - 1.48)]. Children aged 5-14 years were the main reservoir for continuing pneumococcal VT carriage, as they contributed approximately 63% to the overall risk of exposure to VT pneumococci in the population. A significant proportion (49%) of VT exposure in children under 2 years may be associated with contacts with children aged 5-9 years. Those under 2 years old and adults aged 45 years or older each contributed less than 5% to the overall VT pneumococcal carriage exposure in the population. I found that 54% of the residents travel at least once a month to villages ≥ 5km from their residence, spending almost half a day at the places to which they travel. Secondly, I designed and conducted a study to directly observe social contacts of selected children within schools and assessed the accuracy of proxy-reported versus observed physical contact data among schoolchildren who had been enrolled in the social contact and pneumococcal carriage survey. Social contact rates among pupils in rural Gambian schools were high, with a median of 15 contacts during the observation period (IQR: 11–20), and were strongly age-assortative, with most contacts involving physical touch (67.5%). Fifty-eight percent of proxy-reported contacts were underestimated, while 40% were over-reported by at least one contact, respectively. In conclusion, my work demonstrates that while VT carriage has significantly decreased in The Gambia since the introduction of PCV vaccination, residual VT carriage persists, particularly among the 5-14-year-old age group, among whom direct protection from immunisation during infancy has likely waned. Including a booster dose in the PCV vaccination schedule and/or additional booster doses for children at primary school entry may support better control of VT circulation in the population. Further research should be conducted to evaluate the impact of booster doses and a primary school entry PCV dose on VT carriage in regions with residual VT carriage.