Estimating the impact of pneumococcal conjugate vaccines on childhood pneumonia in sub-Saharan Africa: A systematic review

Background The impact of pneumococcal conjugate vaccine introduction in reducing the incidence of childhood pneumonia has not been well documented in sub-Saharan Africa. Many studies evaluating vaccine impact have used invasive pneumococcal disease or pneumococcal pneumonia as an outcome. Objective To estimate the impact of routine administration of 10-valent and 13-valent PCV on the incidence of pneumonia in children under five years of age in sub-Saharan Africa. Data sources A systematic review was conducted between 16 and 31 July 2019. The review was registered on PROSPERO with registration number CRD42019142369. The literature search was conducted in indexed databases including Medline and Embase, grey literature databases and online libraries of two universities. Manual search of the references of included studies was performed to identify additional relevant studies. The search strategy combined pneumococcal conjugate vaccine, pneumonia and child as search concepts. Study selection Studies investigating the impact of 10- or13-valent PCV on childhood pneumonia in a sub-Saharan African country were eligible for inclusion. Case-control, cohort, pre-post and time-series study designs were eligible for inclusion. Exclusion criteria were use of 7- or 9-valent PCV, systematic review studies, clinical trials and record publication prior to 2009. Data extraction Independent data extraction was conducted. Key variables include year study conducted, type of study design, type of PCV used and year of introduction, reported PCV coverage, outcome measure evaluated and the effect measure. Data synthesis Eight records were included in the final analysis, 6 records were pre-post or time-series studies, 1 was a case-control study and 1 report combined pre-post and case-control studies. Vaccine impact measured as percentage reduction in risk (%RR) of clinical pneumonia was mostly small and non-significant. The risk reduction was more significant and consistent on radiological and pneumococcal pneumonia. Vaccine effectiveness reported in case-control studies was mostly non-significant. Conclusion Evidence of the positive impact of routine infant pneumococcal vaccination on pneumonia in sub-Saharan Africa is weak. There is a need for more research in this area to evaluate the influence of pathogen or serotype replacement in pneumonia after PCV introduction. Ongoing surveillance is also required to establish the long term trend in pneumonia epidemiology after PCV introduction.