Adjusted vaccine effectiveness (VE) for 2015–2016 seasonal influenza vaccine against 2009 pandemic influenza A(H1N1) virus (A[H1N1]pdm09) and B(Victoria) virus, by epidemic period, Canadian Sentinel Practitioner Surveillance Network. Stratified estimates were derived using an interaction model based on the entire analytic sample for A(H1N1)pdm09 and B(Victoria); sample sizes for epidemic subgroups are displayed for interest. Abbreviation: CI, confidence interval. ^aAdjusted for age group, sex, comorbidity, province, collection interval, epidemic period (based on month of specimen collection), and vaccination status*epidemic period interaction. Details are provided in Supplement 11.