Effectiveness of the 13-valent pneumococcal conjugate vaccine against medically attended pneumococcal lower respiratory tract infection among older adults: a case-control study.

The 13-valent pneumococcal conjugate vaccine (PCV13) has been recommended for more than a decade for older adults and individuals with chronic medical or immunocompromising conditions. However, real-world evidence on its vaccine effectiveness (VE) in this population especially Low- or Middle-Income Country (LMIC) is limited. This study aimed to evaluate the VE of PCV13 against pneumococcal lower respiratory tract infection (LRTI) among older and high-risk adults.The study was a case-control design using data from a tertiary, university-affiliated hospital between Jan 2014 and Dec 2024. Adults aged ≥ 60 years with medically attended LRTI were included. Cases were defined as culture-confirmed pneumococcal LRTI. Controls were patients with LRTI in whom Streptococcus pneumoniae was not isolated, identified via ICD-10 codes. VE was estimated using logistic regression, comparing odds of PCV13 vaccination between cases and controls. Among 825 patients with LRTI, 39 (4.7%) had received PCV13 and 786 (95.3%) were unvaccinated. The crude VE of PCV13 against pneumococcal LRTI was 71.9% (95% CI: 27.3-89.1), and the adjusted VE was 73.3% (95% CI: 9.0-92.1). The requirement for mechanical ventilation at admission decreased among PCV13-vaccinated patients compared with unvaccinated patients with pneumococcal LRTI. VE appeared comparable among individuals aged ≥ 75 years compared to those < 75 years. In a sensitivity analysis restricted to controls with non-pneumococcal bacterial LRTI, the crude VE increased to 76.1% (95% CI: 34.3-91.3).PCV13 demonstrated real-world effectiveness in preventing medically attended pneumococcal LRTI among older adults. The public health benefit of PCV13 in older adults in LMICs was clearly demonstrated.