Has the change to acellular pertussis vaccine improved or worsened pertussis control?

Between July 1997 and April 1998, all provinces and territories in Canada switched from using a combination vaccine of diphtheria and tetanus toxoids, whole-cell pertussis, inactivated poliovirus and Haemophilus influenzae type b conjugate vaccine (DTwP-IPV-Hib) to a combination vaccine containing acellular pertussis (DTaP-IPV-Hib). In this issue, Vickers and colleagues, (1) using passive surveillance data from the Saskatoon Regional Health Authority in Saskatchewan for the period 1995-2005, report on their analysis of the effect of the change to the new vaccine on the incidence of pertussis among children less than 10 years of age. They found that, among infants (< 1 year old) and preschool children (aged 1-4 years), those who had received either the whole-cell pertussis vaccine or a combination of the whole-cell and acellular pertussis vaccines had a lower incidence of pertussis than those who had received only the acellular vaccine; they found a reverse trend among children 5-9 years of age. Vickers and colleagues concluded that consideration be given to either modifying the current acellular pertussis vaccine or reverting back to using the whole-cell vaccine, perhaps in a sequential DTwP-IPV-Hib/DTaP-IPV-Hib schedule.

Do the findings of their study coincide with those from other analyses of the transition from whole-cell to acellular pertussis vaccine in Canada? Canada has had a high incidence of pertussis since 1989, and studies have shown that the Canadian whole-cell pertussis vaccine introduced in the 1980s had low effectiveness rates. (2-4) As a result, a cohort effect that moved yearly affected more and …