Quality of HMO vaccination databases used to monitor childhood vaccine safety

The availability of large, population-based, automated, medical care databa ses provides unique opportunities for monitoring the safety of childhood va ccines. The authors assessed the quality of automated vaccination databases by comparing them with vaccinations documented in paper-based medical reco rds at three large US West Coast health maintenance organizations (HMOs) pa rticipating in the Vaccine Safety DataLink (VSD) study, a Centers for Disea se Control and Prevention collaborative study of childhood vaccine safety. The authors randomly selected 1% or 2% samples of VSD study populations (n = 1,224-2,577) for data quality analyses. Agreement between automated and a bstracted vaccinations required identical triads of child identification nu mber, vaccination date, and vaccine type. Separate analyses were conducted for each HMO and for each Vaccine type administered between 1991 and 1995. Agreement was measured by three matching proportions: 1) the proportion of automated vaccinations present in the abstracted source, 2) the proportion of abstracted vaccinations present in the automated source, and 3) the prop ortion of vaccinations from either source present in both sources. Overall, for common childhood vaccines, proportion 1 ranged from 83% to 99%, propor tion 2 ranged from 82% to 98%, and proportion 3 ranged from 70% to 97%. Lac k of automated data was the most frequent type of discrepancy, followed by date mismatches and vaccine type mismatches. Vaccination exposure classific ation errors in the range reported here were found by mathematical modeling to only modestly bias measured medical outcome rate ratios toward the null hypothesis. The results of the data quality analyses support the usefulnes s of vaccination exposure data derived from these automated HMO vaccination databases.