Vaccine safety implications of Ontario, Canada's switch from DTaP-IPV to Tdap-IPV for the pre-school booster

Ontario, Canada, replaced the 4-6 year old diphtheria (D, d), tetanus (T), acellular pertussis (aP, ap) and polio (IPV) booster from DTaP-IPV to Tdap-IPV in May 2012. We assessed the impact of this replacement on the rate and types of reported adverse events following immunization (AEFIs). We used AEFIs reported among 4-6 years olds, through the provincial surveillance system, following administration of DTaP-IPV or Tdap-IPV from 2009 to 2013. Reporting rates per 100,000 doses distributed were calculated using publicly funded doses distributed as the denominator. A total of 204 AEFIs were reported (DTaP-IPV, n = 182; Tdap-IPV, n = 22). AEFI reporting rates were 33.1 and 6.3 per 100,000 doses distributed for DTaP-IPV and Tdap-IPV, respectively. Injection site reaction rate was lower for Tdap-IPV compared with DTaP-IPV (1.7 vs 20.6 per 100,000 doses). The replacement resulted in a decline in the number of reports and AEFI reporting rates, most notably a substantial decrease in injection site reactions.