Assessing pneumococcal revaccination safety among New York State Medicare beneficiaries.

Objective. There have not been adequate studies of the safety of pneumococcal revaccination, especially for revaccination at intervals of less than five years. The objective of this study was to assess revaccination safety by determining whether pneumococcal revaccination is associated with greater utilization of postvaccination health care, compared with initial vaccination. Methods. The authors conducted a retrospective cohort study of 119,990 New York State Medicare beneficiaries 65 years of age and older who received pneumococcal vaccinations from February 1, 1999, through December 17, 1999. The study used a multivariate regression model with three primary outcome measures-emergency room visits, hospitalizations, and office visits during the two weeks postvaccination. Secondary outcome measures were specific International Classification of Diseases, Ninth Revision, Clinical Modification (ICD-9-CM) codes potentially related to adverse vaccine reactions. Results. Of 119,990 patients, 23,663 had previous claims for pneumococcal vaccination, including 13,466 for whom the revaccination interval was less than five years. After adjustment for demographic and comorbidity factors, revaccination at less than five years was associated with higher rates of emergency room visits (odds ratio [OR] = 1.17; 95% confidence interval [Cl] 1.02, 1.34) and office visits (OR = 1.13; 95% Cl 1.09, 1.18) during the two-weeks postvaccination, compared with initial vaccination. In addition, several ICD-9-CM codes that might indicate vaccine reactions were recorded more frequently for the revaccination group than for the comparison group. Conclusions. Because of potential policy implications, further investigation is needed of the causes and consequences of short-interval revaccination.