A multicentre case-control study about effectiveness of pneumococcal vaccination against pneumonia hospitalization in at-risk adults

BACKGROUND: Community-acquired pneumonia (CAP) is a leading cause of morbidity in adults with chronic conditions. Although pneumococcal vaccine effectiveness (VE) has been demonstrated in older adults, evidence is scant regarding adults < 65 years. We evaluated pneumococcal VE against CAP-related hospitalization in at-risk adults aged 18–64 years. METHODS: We conducted a multicentre case-control study in Spain (2020–2024). Cases were adults aged 18–64 years with risk conditions, hospitalized for ≥ 24 h, with radiological and clinical patterns compatible with CAP. Controls were hospitalized patients with risk conditions but without pneumonia. Vaccination status was classified as 23-valent pneumococcal polysaccharide vaccine only, pneumococcal conjugate vaccine only, sequential vaccination, or unvaccinated. Logistic regression was used to estimate crude and adjusted odds ratio (OR) values, with VE calculated as (1–OR) × 100. Analyses were stratified by immune status, and a sensitivity analysis was performed excluding SARS-CoV-2 cases. RESULTS: We included 805 cases and 806 controls. None of the pneumococcal vaccination strategies showed significant effectiveness against hospitalization for CAP. In immunocompromised individuals, 23-valent pneumococcal polysaccharide vaccine showed significantly negative adjusted VE (-142.0, 95%CI: -504.4 to -1.1). Excluding SARS-CoV-2 cases yielded similar estimates. CONCLUSIONS: Pneumococcal vaccination was not associated with a reduced hospitalization risk for CAP in adults aged 18–64 years with risk conditions.