Background: In 2013 the Institute of Medicine suggested that the Vaccine Safety DataLink (VSD) should broaden its population by including data of more patients from low income and racially and ethnically diverse backgrounds. In response, Kaiser Permanente Colorado (KPCO) partnered with Denver Health (DH), an integrated safety net health care system, to explore the integration of DH data.

Methods: We compared three different methods (reference date of September 1, 2013): "Empanelment" (any patient who has had a primary care visit in the past 18months), "Proxy-enrollment" (two health care visits in 3years separated by 90days), and "Enrollment" in a managed care plan. For each of these methods, we compared cohort size, vaccination rates, socio-demographic characteristics, and health care utilization.

Results: The empaneled population at DH provided the best comparison to KPCO. DH's empaneled population was 111,330 (57,173 adults; 54,157 children), while KPCO had 436,290 empaneled patients (336,462 adults; 99,828 children). Vaccination rates in both health care systems for empaneled patients were comparable. Two year-old up-to-date coverage rates were 83.2% (KPCO) and 86.9% (DH); rates for adolescent Tdap and MCV4 were 85.5% (KPCO) and 90.6% (DH). There were significant differences in the two populations in age, gender, race, preferred language, and % Federal Poverty Level (FPL) (DH 70.7%<100% FPL; KPCO 17.4%), as well as in healthcare utilization - for example pediatric emergency department utilization was twice as high at DH.

Conclusions: Using a cohort of "empaneled" patients, it is possible to integrate data from a safety net health care system that does not have a uniform managed care population into the VSD, and to compare vaccination rates, socio-demographic characteristics, and health care utilization across the two systems. The KPCO-DH collaboration may serve as a model for incorporating data from a safety net healthcare system into the VSD.