The effectiveness of the polysaccharide pneumococcal vaccine for theprevention of hospitalizations due to Streptococcus pneumoniaecommunity-acquired pneumonia in the elderly differs between thesexes : results from the Community-Acquired PneumoniaOrganization (CAPO) international cohort study

Background: The effectiveness of the 23-valent pneumococcal polysaccharide vaccine (PPV23) to prevent hospitalizations due to Streptococcus pneumoniae community-acquired pneumonia (SpCAP) is controversial. Recent literature suggests that vaccine effectiveness may be influenced by sex. In this study, we define the effectiveness of prior PPV23 vaccination for the prevention of hospitalizations due to SpCAP, and evaluate the impact of sex on this effectiveness. Methods: This was a nested case-control study from the CAPO international cohort study database. SpCAP was defined as CAP plus S. pneumoniae identified in blood, bronchoalveolar lavage, sputum, or urinary antigen. Vaccination with PPV23 prior to hospitalization was defined as documented in the medical record. A propensity score-weighted logistic regression model was used to calculate odds ratios. The adjusted vaccine effectiveness (aVE) was calculated as 1-adjusted odds ratio. Results: From a total of 2688 elderly adult hospitalized patients with CAP, SpCAP was identified in 279 (10%). The overall aVE was 37% (95% CI: 10.1-55.4%, P= 0.01). For males, the aVE was 34% (95% CI:-1.0% to 57.3%, P= 0.06). For females the aVE was 68% (95% CI: 40.3-83.0%, P= 0.001). Conclusions: PPV23 protects elderly patients from hospitalization due to SpCAP, but female sex drives the effectiveness. Future analysis of vaccine trials should consider the importance of sex as a stratification factor