Prior Pneumococcal Vaccination is Associated with Reduced Death, Complications, and Length of Stay among Hospitalized Adults with Community-Acquired Pneumonia. Fisman DN, Abrutyn E, Spaude KA, Kim A, Kirchner C and Daley J. Clinical Infectious Diseases, 2006;42 (8):1093-1101.
Does prior immunization with the 23-valent pneumococcal polysaccharide vaccine improve clinical outcomes among adult patients hospitalized with community-acquired pneumonia?
The researchers collected data from 68,289 consecutive patients hospitalized for community-acquired pneumonia (CAP) between September 1999 and December 2003. The patients studied were admitted to Tenet Healthcare hospitals geographically concentrated in the Gulf Coast and California with several additional hospitals in the Midwest and Pennsylvania. CAP was defined according to diagnostic coding standards.
Information, including known risk factors for CAP, was abstracted by case managers at the time of hospitalization. The PORT score of illness severity that predicts CAP outcome at 30 days by dividing patients into five risk categories was utilized. Prior immunization with the 23-valent pneumococcal polysaccharide vaccine (PPV23) was examined as an independent factor to determine if the numbers of deaths, complications, and prolonged hospitalizations were significantly reduced.
A total of 62,918 of the 68, 289 patients met study criteria for inclusion. Of these, 7,390 patients had received PPV23 (12%) prior to admission and 14,585 (23%) were documented to have not received PPV23; the remainder were of unknown PPV23 immunization status.
Vaccinated patients were sicker, but younger and less likely to have underlying illnesses, to smoke, or to be nursing home residents than the unvaccinated or unknown vaccine status groups. PPV23 vaccinated patients were much more likely to have also received influenza vaccine within the preceding 12 months.
The patients who were PPV23 vaccinated were 40-70% less likely to die of any cause during hospitalization even after adjustment for recognized mortality risk factors. Vaccination also appeared to reduce the risk of respiratory failure and other complications and reduced length of stay by about 2 days.
This study indicates a reduction in the likelihood of death, complications, and duration of hospital stay for CAP patients who had previously received PPV23.
Approximately 70% of the CAP population studied had an unknown PPV23 immunization status, consistent with the lack of a strong national adult immunization infrastructure.
The study lacks microbiologic confirmation of infection with Streptococcus pneumoniae and serologic documentation of the types of S. pneumoniae involved in the cases. Thus, it is not possible to determine unequivocally whether the reduction in mortality was specifically due to reduction in cases of pneumococcal pneumonia caused by serogroups in the 23-valent vaccine.
The use of hospitalized CAP patients as the population of interest might well underestimate the impact of PPV23 immunization, since those who were previously immunized would be expected to be less likely to have serious pneumococcal disease and less likely to have been admitted to the hospital.