EFFECTIVENESS OF PNEUMOCOCCAL CONJUGATE VACCINES IN PREVENTING PNEUMONIA IN CHILDREN: A SYSTEMATIC REVIEW AND META-ANALYSIS OF RANDOMIZED CLINICAL TRIALS

Abstract

Background: Pneumonia remains a leading cause of mortality in children under five years old worldwide, with Streptococcus pneumoniae identified as the most common bacterial pathogen. The documented effectiveness of pneumococcal conjugate vaccines (PCVs) varies considerably depending on the diagnostic criteria used. Objective: To evaluate the efficacy of PCVs in preventing pneumonia in children, focusing on differences between clinical and radiologically confirmed outcomes. Methods: A systematic review and meta-analysis of randomized controlled trials (RCTs) was conducted in accordance with the PRISMA guidelines. Comprehensive searches were performed across PubMed, Embase, and Cochrane CENTRAL. Pooled risk ratios (RRs) with 95% confidence intervals (CIs) were calculated using a random-effects model. Results: Four large-scale RCTs involving over 120,000 children were included in the final analysis. PCVs significantly reduced radiologically confirmed pneumonia, with vaccine efficacy (VE) ranging from 20% to 45%. In contrast, the efficacy against clinical pneumonia was limited (ranging from -1.2% to 26.3%), primarily due to the dilution effect caused by non-pneumococcal etiologies. Furthermore, PCVs demonstrated robust protection against invasive pneumococcal disease (IPD) and contributed to substantial reductions in hospitalizations and antibiotic consumption. Protective effects were consistently observed across diverse populations, including high-risk groups. Conclusion: PCVs are highly effective in preventing severe pneumonia in children, particularly when evaluated using radiological criteria. Standardized outcome definitions are essential for accurately estimating true vaccine impact in public health.