Pneumococcal vaccination and aspiration pneumonia in super-aged societies: A scoping review of the evidence landscape

Abstract

Aspiration pneumonia is the leading cause of pneumonia-related death in Japan, where 29.3% of the population is aged ≥ 65 years, and it represents a growing challenge across rapidly aging Asian societies. Although pneumococcal vaccination is widely implemented for older adults, its effectiveness specifically against aspiration pneumonia remains unestablished. This scoping review systematically mapped the existing evidence on pneumococcal vaccination effectiveness for aspiration pneumonia prevention. Following Preferred Reporting Items for Systematic Reviews and Meta-Analyses extension for Scoping Reviews (PRISMA-ScR) guidelines, PubMed, Cochrane Library, and Cumulative Index to Nursing and Allied Health Literature (CINAHL) were searched, identifying five studies (three primary studies and two reviews). None directly evaluated vaccine effectiveness with aspiration pneumonia as a defined outcome. Indirect evidence from studies including aspiration pneumonia within composite pneumonia outcomes suggests potential benefits; however, vaccine-specific effects could not be isolated. This review identifies a structural misalignment between the predominant pneumonia phenotype in super-aged societies and existing vaccine evaluation frameworks, and demonstrates that aspiration pneumonia has been systematically overlooked as a prespecified outcome in vaccine effectiveness research. Notably, the absence of direct evidence reflects limitations in study design and outcome definition, rather than evidence of vaccine ineffectiveness. Dedicated clinical studies are warranted to inform evidence-based immunization policies.