Evaluating Confounding Control in Estimations of Influenza Antiviral Effectiveness in Electronic Health Plan Data

Observational studies of oseltamivir and influenza complications could suffer from residual confounding. Using negative control risk periods and a negative control outcome, we examined confounding control in a claims-based study of oseltamivir and influenza complications (pneumonia, all-cause hospitalization, antibiotic dispensing). Within the FDA's Sentinel System we identified individuals ≥18 years initiating oseltamivir on the influenza diagnosis date versus those who did not, during three influenza seasons (2014-2017). We evaluated primary outcomes in the following 1-30 days (primary risk period) and 61-90 days (negative control period), and non-vertebral fractures (negative control outcome) in days 1-30. We estimated propensity score-matched risk ratios (RR) per season.