A resurgence of pertussis cases among immunized and unimmunized individuals raised questions about vaccine effectiveness and waning immunity. We performed a test-negative case-control study, utilizing Ontario administrative and laboratory data. We used crude and adjusted multivariable logistic regression models to estimate odds ratios (ORs) comparing the odds of cases being vaccinated against that of controls. Vaccine effectiveness was calculated as (1-OR)x100. There were 5,867 individuals available for analysis (486 test-positive cases and 5,381 test-negative controls). Vaccine effectiveness was 80% (95%CI, 71%-86%), 84% (95%CI, 77%-89%), 62% (95%CI, 42%-75%), and 41% (95%CI, 0-66%) at 15-364 days, 1-3 years, 4-7 years, and ?8 years since last immunization, respectively. The odds of developing pertussis increased 27% (95%CI, 20%-34%) per year from last immunization. Acellular, compared to whole cell, vaccine priming was associated with a two-fold increased risk of pertussis. These results have important policy implications for optimizing pertussis control and to spur vaccine development.