Effectiveness of the 23-Valent Pneumococcal Polysaccharide Vaccine (PPV23) in Preventing Community-Acquired Pneumonia in Adults: A Population-Based Cohort Study.

Aim: The aim was to assess the effectiveness of 23-valent pneumococcal polysaccharide vaccine (PPV23) in preventing CAP in adults.
Methods: This was a population-based cohort study, followed up over 5 years (2015-2019), that included 47,768 persons aged ≥18 years assigned to three primary care centres. Data were retrospectively obtained from electronic medical records and databases. The vaccination effect was adjusted for potential confounders. Analyses were performed for the entire study population and for the ≥65 age subgroup.
Results: The annual incidence of CAP (per 10 ³ adult inhabitants) was 3.29 overall, and 8.08 and 2.93 for vaccinated and non-vaccinated persons, respectively. The non-adjusted effect of PPV23 on CAP was evidenced by HR = 2.80 (95% CI: 2.32-3.37), and after adjusting for possible confounders, PPV23 showed no significant independent effect on CAP in the overall population (HR = 1.14; p = 0.277) or in persons aged ≥65 years (HR = 1.30; p = 0.051). No protective effect was observed in persons vaccinated <2 years previously (HR = 1.17; p = 0.514).
Conclusions: PPV23 showed no effect in preventing CAP in adults aged ≥18 years or in the subgroup aged ≥65 years, even if vaccinated <2 years previously.