Evaluating the safety of influenza vaccine using a claims-based health system

Abstract Introduction As part of the Centers for Disease Control and Prevention's monitoring and evaluation activities for influenza vaccines, we examined relationships between influenza vaccination and selected outcomes in the 2009–2010 and 2010–2011 influenza seasons in a claims-based data environment. Methods We included patients with claims for trivalent influenza vaccine (TIV) and/or 2009 pandemic influenza A H1N1 vaccine (H1N1) during the 2009–2010 and 2010–2011 influenza seasons. Patients were followed for several pre-specified outcomes identified in claims. Seizures and Guillain–Barre Syndrome were selected a priori for medical record confirmation. We estimated incidence rate ratios (IRR) using a self-controlled risk interval (SCRI) or a historical comparison design. Outcomes with elevated IRRs, not selected a priori for medical record review, were further investigated with review of claims histories surrounding the outcome date to determine whether the potential event could be ruled-out or attributed to other causes based on the pattern of medical care. Results In the 2009–2010 season, no significant increased risks for outcomes following H1N1 vaccination were observed. Following TIV administration, the IRR for peripheral nervous system disorders and neuropathy was slightly elevated (1.07, 95% CI: 1.01–1.13). The IRR for anaphylaxis following TIV was 28.55 (95% CI: 3.57–228.44). After further investigation of claims histories, the majority of potential anaphylaxis cases had additional claims around the time of the event indicating alternate explanatory factors or diagnoses. In the 2010–2011 season following TIV administration, a non-significant elevated IRR for anaphylaxis was observed with no other significant outcome findings. Conclusion After claims history review, we ultimately found no increased outcome risk following administration of 998,881 TIV and 538,257 H1N1 vaccine doses in the 2009–2010 season, and 1,158,932 TIV doses in the 2010–2011 season.