|dc.description.abstract||Abstract: Background: Pneumococcal diseases are responsible for over 1 million deaths every year and most of these are children in sub-Saharan Africa. The 7-valent pneumococcal conjugate vaccine (PCV7) has recently been introduced into child immunisation schedule in The Gambia. Early age at acquisition and high pneumococcal serotype diversity in The Gambia demand close monitoring after PCV7 introduction.
Objective: To determine the impact of community vaccination with PCV7 on nasopharyngeal carriage of pneumococci in newborn infants up to the age of 8 weeks.
Methods: Twenty one representative rural Gambian villages were randomly allocated to intervention and control groups. One dose of PCV7 was given to older children and adults, 2 doses for children aged 12 – 30 months and 3 doses for infants less than 12 months of age. In control villages, PCV7 was given to those aged 30 months and below and one dose of meningococcal group C conjugate vaccine (MnCC) was given to those >30 months of age. Babies born during the trial were recruited and nasopharyngeal swabs (NPS) collected as soon after delivery as possible and then weekly till end of 8 weeks. Transport and processing of NPS were by standard methods. Prevalence and rates of acquisition of any pneumococcus, vaccine serotypes (VT), vaccine associated serotypes (VAT), non-vaccine serotypes (NVT) and non-typeable pneumococci (NT) were studied. Kaplan-Meier failure functions were used to study time to first acquisition of pneumococci and acquisition rates were compared using Cox regression model adjusting for clustering at village level.
Results: One hundred eighty nine and 155 infants were recruited in intervention and control villages respectively. Overall prevalence of carriage by the 8th week of life was 75% and 80% in intervention and control arms respectively. Sixty seven serotypes were isolated in the study. Prevalence of VT carriage was significantly lower in intervention villages compared to control (11.1% vs. 27.4%, p<.001). NVT carriage was higher in intervention villages (68.3% vs. 60.6%, p=0.141) and there were statistically significant differences in the carriage rates of individual NVT; 7F (2.5% vs. 1.1%, p=.016), 10A (3.9% vs. 2.3%, p=.026) and 15B (4% vs. 1.6%, p=.001) in intervention compared to control villages. VAT and NT carriage were similar in both arms. The risk of acquisition of VT was significantly lower in intervention compared to control villages (hazard ratio 0.37; 95%CI 0.22 – 0.6, p<.001). For the NVT, risk of acquisition was higher in intervention villages compared to controls but was not statistically significant (hazard ratio 1.26; 96CI 0.94 – 1.68, p=.12). There was a slight but non-significant increased risk of acquisition of NT in intervention compared to control villages (hazard ratio 1.13; 95%CI 0.61 – 2.09). VAT 6A carriage was significantly lower in intervention compared to control villages (1.8% vs. 4% respectively, p=.002) and VAT 19A carriage was higher in intervention villages compared to controls but this was not statistically significant (2.3% vs. 1.6% respectively, p=.205). The presence of children <5years of age was associated with an increased risk of acquisition of VAT (hazard ratio 1.07; 95%CI 1.03 – 1.12, P<.001).
Conclusion: High immune pressure through community vaccination with PCV7 in The Gambia resulted in a significant ‘indirect’ reduction in the carriage of pneumococci of vaccine serotypes in infants in their first 8 weeks of life in these communities. This was associated with increased acquisition of pneumococci of non-vaccine serotypes. These findings support both the introduction of PCV7 into The Gambia and the need for ongoing active surveillance.||