Poster Presentation Lancefield International Symposium for Streptococci and Streptococcal Diseases 2025

Distribution of pneumococcal serotypes causing invasive disease and carriage in rural Gambia in the post-vaccination era (#72)

Baleng Mahama Wutor 1 , Isaac Osei 1 2 , Ilias M Hossain 1 , Williams Adefila 1 , Abdulsalam Yusuf 1 , Rasheed Salaudeen 1 , Molfa Minteh 1 , Ousman Barjo 1 , Grant A Mackenzie 1 2
  1. Medical Research Council Unit The Gambia at London School of Hygiene and Tropical Medicine, Fajara, KMC, Gambia
  2. Faculty of infectious and tropical diseases, London School of Hygiene and Tropical Medicine, London, United Kingdom

Background

Pneumococcal Conjugate Vaccines (PCVs) have significantly reduced the incidence of invasive pneumococcal disease (IPD). However, the predominance of non-vaccine type (NVT) pneumococci highlights the ongoing need for pneumococcal surveillance.

This study characterized the epidemiology and serotype distribution of Streptococcus pneumoniae in sick children in The Gambia. PCV 7 was introduced in The Gambia in 2009 and replaced by PCV13 in 2011.

Methods

A secondary analysis of pneumococcal surveillance data collected between 2015 and 2023 was performed. Children under 5 years with suspected IPD were investigated according to standardised criteria. Pneumococci were serotyped according to WHO guidelines. Poisson regression was used to assess the trend in annual incidence of IPD over the study period.

Results

The IPDs detected during the period were 151. The incidence rate in 2023 was 64.1% lower than in 2015, with an incidence rate ratio (IRR) of 0.359 (95% CI: 0.178 - 0.719, p = 0.002). The predominant serotypes causing IPD and those isolated in carriage were mostly NVTs (80.3% and 86.7% respectively). While pneumococcal serotypes 12F, 35B, 46, 2, 14, and 45 were the commonest causes of IPD, serotypes 35B, 13, 14, 15B, 21, and 12F were common in carriage. Only 53.8% of pneumococcal serotypes that caused IPD were homologous with paired carriage serotypes.

Conclusion

The burden of IPDs in The Gambia is predominantly driven by NVT pneumococcal serotypes. Though PCVs are effective, continued IPD surveillance in Africa is needed to monitor serotype replacement and inform the development of higher-valency vaccines.

 

  1. Mackenzie et al. Impact of the introduction of pneumococcal conjugate vaccination on invasive pneumococcal disease and pneumonia in The Gambia: 10 years of population-based surveillance. The Lancet Infectious Diseases. 2021;21(9):1293-302.
  2. Lo et al. Pneumococcal lineages associated with serotype replacement and antibiotic resistance in childhood invasive pneumococcal disease in the post-PCV13 era: an international whole-genome sequencing study. The Lancet Infectious Diseases. 2019;19(7):759-69
  3. Balsells et al. Serotype distribution of Streptococcus pneumoniae causing invasive disease in children in the post-PCV era: a systematic review and meta-analysis. PloS one. 2017;12(5):e0177113