Postlicensure Surveillance for Pneumococcal Invasive Disease
Objective: To assess the direct and indirect effects of the introduction of routine use of pneumococcal conjugate vaccine in infants and toddlers at risk for invasive disease caused by vaccine serotypes and nonvaccine serotypes in vaccinated children and unvaccinated children of the same age. Secondary objectives included determination of the risk of pneumococcal infections in unvaccinated older children and adults in the same population and the impact of vaccine introduction on patterns of antimicrobial resistance.
Methods: Northern California Kaiser Permanente provides integrated comprehensive care to 3.1 million people and has an annual birth cohort of 38,000 infants. Microbiology services use a regional laboratory. Automated laboratory results, immunization records as well as diagnoses for inpatient and outpatient utilization are available from clinical data bases. Beginning in April 2000, the heptavalent pneumococcal conjugate (PNCV7) vaccine was introduced into routine use in the Northern California Kaiser Permanente population. Cases of invasive pneumococcal disease were identified from the automated hospital diagnosis as well as laboratory databases for all individuals, vaccinees and nonvaccinees, inpatient and outpatient. For the purpose of these analyses, pneumococcal invasive disease was defined as a positive culture from a normally sterile site.
Results: As of March 2003, 157,471 children had received 1 dose or more of PNCV7, but only 24% of those <2 years of age received all 4 doses as a result of shortages of vaccine. During the last year of observation, no cases of vaccine serotype disease were seen in children <1 year of age compared with an incidence ranging between 51.5 and 98.2 cases per 100,000 person-years (16-34 cases per year) in the years before vaccine introduction. Similar reductions were seen in children <5 years of age. There was no evidence of any concomitant increase in pneumococcal disease caused by nonvaccine serotypes. High level resistance of pneumococci to penicillin fell from a peak of 15% in 2000 to 5% in the first half of 2003. Similar trends were seen for other antibiotics.
Conclusion: The PNCV7 vaccine is highly effective in reducing the burden of pneumococcal disease in children <5 years of age, and there is evidence of a herd effect as well as a decrease in the antibiotic resistant in strains causing disease. For invasive disease, there is no current evidence of serotype replacement.

Heptavalent pneumococcal conjugate vaccine (PNCV7; Prevnar, Wyeth) was approved for use in infants in February 2000, the result of an evaluation of 37,868 infants in whom the vaccine was found to be safe and effective for invasive disease, otitis media and pneumonia. The vaccine contains polysaccharide conjugates of serotypes 4, 6B, 9V, 14, 18C, 19F and 23F. This report details results of a 3.5-year surveillance of pneumococcal infection after licensure of PNCV7 in a large, defined United States population from which the study children were drawn. The Northern California Kaiser Permanente (NCKP) population consists of an annual birth cohort of 38,000 infants and a total health plan population of 3.1 million. During the observation period, the entire population was under surveillance, including children and adults, to assess both direct and indirect effects of the vaccination program.