because of loss to follow-up, emigration, or death. The rate ratio for type 1 diabetes diagnosis any time after at least one dose of combined DTaP-IPV vaccine (compared to the unvaccinated) was 0.96 (95% CI, 0.71–1.30). The study also evaluated the rate ratios of diabetes diagnosis 1, 2, 3, 4, and > 4 years after DTaP-IPV vaccination and found no significant differences. The authors concluded that DTaP-IPV vaccination does not increase the risk of type 1 diabetes in children.

Klein et al. (2010) conducted a cohort study in children (10 to 18 years of age) enrolled in the Northern California Kaiser Permanente (NCKP) Health Care Plan. Children who received a Tdap vaccination during September 2005 through December 2006 were included in the analysis and monitored for type 1 diabetes diagnoses for the 6 months following vaccination (ending in June 2007). To identify new cases of diabetes, no diagnoses could appear in the medical records during the year before vaccination. The study identified a historical NCKP comparison cohort who received a Td vaccination from June 2002 through September 2005, and was matched to the Tdap cohort on age, sex, geographic location, and season of vaccination. Each cohort included 12,509 children for a total of 25,018 study participants. The matched odds ratio for type 1 diabetes diagnosis within 6 months following Tdap vaccination (compared to type 1 diabetes within 6 months of Td vaccination) was 0.333 (95% CI, 0.006–4.151). However, only one event and three events of diabetes were observed in the Tdap and Td cohorts, respectively, which resulted in low statistical power to detect an association. The authors concluded that Tdap vaccination does not increase the risk of type 1 diabetes in children compared to Td vaccination, which only provides information on the safety of the acellular pertussis antigen component.

Weight of Epidemiologic Evidence

The five observational studies consistently report no increased risk of type 1 diabetes following vaccination with diphtheria toxoid, tetanus toxoid, and acellular pertussis antigens alone or in combination; two studies had negligible limitations (Patterson et al., 2000; Hviid et al., 2004). The five studies had relatively large sample sizes and were representative of European and U.S. populations of children across a broad range of ages and varying time periods at risk of type 1 diabetes following vaccination. See Table 10-5 for a summary of the studies that contributed to the weight of epidemiologic evidence.

The committee has a high degree of confidence in the epidemiologic evidence based on five studies with validity and precision to assess an association between diphtheria toxoid–, tetanus toxoid–, or



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