Incidence of invasive pneumococcal disease among children after introduction of a 7-valent pneumococcal conjugate vaccine: A population-based study in Olmsted County, Minnesota

OBJECTIVE: To examine the effect of the 7-valent pneumococcal conjugate vaccine in a well-characterized population in Olmsted County, Minnesota, with a combination of urban and rural residents likely to have a relatively low risk of invasive pneumococcal disease (IPD). PATIENTS AND METHODS: This population-based study analyzed data from children younger than 5 years to determine the incidence of IPD from January 1, 1995, to December 31, 2007. RESULTS: From 1995 through 2007, 29 cases of IPD were identified in the study population, but 2 patients denied research authorization; thus, 27 cases were available for review. From 1995-1999 to 2001-2003, the incidence of IPD decreased from 33.5 (95% confidence interval [CI], 16.6-50.5) to 10.8 (95% CI, 0.0-23.0) cases per 100,000 person-years (68% decrease; P=.046). The incidence subsequently increased to 15.2 (95% CI, 3.0-27.4) cases per 100,000 person-years from 2004 through 2007; however this change was not significant (P=.62). All cases of IPD with available serotype data from 2002 through 2007 (n=5) were due to non-7-valent conjugate vaccine serotypes. CONCLUSION: Although the baseline incidence of IPD was much lower than that reported in other populations, the overall incidence of IPD decreased significantly in children younger than 5 years after introduction of a 7-valent conjugate vaccine.