Efficacy of zinc as adjunctive pneumonia treatment in children aged 2 to 60 months in low-income and middle-income countries: a systematic review and meta-analysis

BACKGROUND: Despite advances in vaccination and case management, pneumonia remains the single largest contributor to early child mortality worldwide. Zinc has immune-enhancing properties, but its role in adjunctive treatment of pneumonia in low-income and middle-income countries (LMICs) is controversial and research still active. METHODS: Systematic review and meta-analysis of randomised controlled trials of zinc and placebo in pneumonia in children aged 2 to 60 months in LMICs. Databases included MEDLINE, the Cochrane Library, EMBASE, LILACS, SciELO, the WHO portal, Scopus, Google Scholar and ClinicalTrials.gov. Inclusion criteria included accepted signs of pneumonia and clear measure of outcome. Risk of bias was independently assessed by two authors. ORs with 95% CI were used for calculating the pooled estimate of dichotomous outcomes including treatment failure and mortality. Time to recovery was expressed as HRs. Sensitivity analyses considering risk of bias and subgroup analyses for pneumonia severity were performed. RESULTS: We identified 11 trials published between 2004 and 2019 fulfilling the a priori defined criteria, 7 from South Asia and 3 from Africa and 1 from South America. Proportional treatment failure was comparable in both zinc and placebo groups when analysed for all patients (OR 0.95 (95% CI 0.80 to 1.14)) and only for those with severe pneumonia (OR 0.93 (95% CI 0.75 to 1.14)). No difference was seen in mortality between zinc and placebo groups (OR 0.64 (95% CI 0.31 to 1.31)). Time to recovery from severe pneumonia did not differ between the treatment and control groups for patients with severe pneumonia (HR 1.01 (95% CI 0.89 to 1.14)). Removal of four studies with high risk of bias made no difference to the conclusions. CONCLUSION: There is no evidence that adjunctive zinc treatment improves recovery from pneumonia in children in LMICs. TRIAL REGISTRATION NUMBER: CRD42019141602.