Effect of pneumococcal vaccination: A comparison of vaccination rates in patients with bacteremic and nonbacteremic pneumococcal pneumonia

Background. Despite the widespread acceptance of the 23-valent pneumococcal capsular polysaccharide vaccine (PPV), its protective effect continues to be disputed. We describe a novel approach to examine the protective effect of this vaccine. Methods. We recorded the vaccination status of every patient for whom a culture yielded Streptococcus pneumoniae during a 4.5-year period, comparing rates of prior PPV administration in patients with (1) bacteremic pneumococcal pneumonia, (2) all-invasive pneumococcal disease, (3) nonbacteremic pneumococcal pneumonia, (4) acute exacerbation of chronic bronchitis (AECB) due to S. pneumoniae, and (5) pneumococcal colonization. The principal comparisons were with patients who had bacteremic pneumonia or any invasive pneumococcal disease and those with nonbacteremic pneumococcal pneumonia. We also compared vaccination rates in patients who had nonbacteremic pneumonia with vaccination rates in patients with AECB or pneumococcal colonization. Results. The rate of prior PPV vaccination was lower among patients with bacteremic pneumococcal pneumonia (39.7%) or any invasive pneumococcal disease (38.0%) than among patients with nonbacteremic pneumonia (57.6%), AECB (60.0%), or pneumococcal colonization (57.8%). PPV conferred a 54% protection rate against bacteremic versus nonbacteremic pneumococcal pneumonia. There was no apparent protection against nonbacteremic pneumonia compared, for example, with colonized persons or with those who had AECB. Conclusions. PPV provides moderate protection against invasive pneumococcal disease but does not protect against nonbacteremic pneumococcal pneumonia. These findings suggest the importance of a continued search for a better pneumococcal vaccine.