Clinical effectiveness of 23-valent pneumococcal polysaccharide vaccine against pneumonia in middle-aged and older adults: a matched case-control study.

The 23-valent polysaccharide pneumococcal vaccine is currently recommended in elderly and high-risk adults. Its efficacy against invasive pneumococcal disease has been demonstrated, but its effectiveness in preventing pneumonia remains uncertain. This study assessed the clinical effectiveness of vaccination against pneumonia among middle-aged and older adults. We conducted a population-based case-control study including 304 case patients over 50 years old with radiographically confirmed pneumococcal pneumonia (94 bacteremic and 210 nonbacteremic cases) and 608 outpatient control subjects (matched by primary care centre, age, sex and risk stratum). Adjusted odds ratios (ORs) for vaccination were calculated using conditional logistic regression, controlling for underlying conditions. Vaccine effectiveness against all pneumococcal pneumonia was 48% (OR: 0.52; 95% confidence interval [CI]: 0.37-0.73). Vaccination was effective against bacteremic cases (OR: 0.34; 95% CI: 0.27-0.66) as well as nonbacteremic cases (OR: 0.58; 95% CI: 0.39-0.86). Vaccine effectiveness was highest against bacteremic infections caused by vaccine types (OR: 0.24; 95% CI: 0.09-0.66). These findings confirm the effectiveness of the vaccine against invasive disease, but they also support the benefit of vaccination in preventing nonbacteremic pneumococcal pneumonia.