To the Editor The modeling study of DeAngelis et al¹ suggested that substitution of 1 dose of whole-cell pertussis vaccine for the first dose of acellular vaccine at age 6 to 8 weeks would result in at least a 91% reduction in the incidence of pertussis. As noted in the accompanying editorial, the validity of these findings relies on both explicit and implicit assumptions within the model structure and its parameters. We go further to say that such a profound effect on pertussis disease and transmission seems inherently unlikely and that implementation barriers are understated.

The assumption driving the model is that acellular pertussis vaccine protects against disease but has no effect on infection and therefore transmission, whereas a single dose of whole-cell vaccine has a strong effect on both disease and infection. Although Warfel et al² showed that whole-cell vaccinated but not acellular vaccinated baboons are protected against asymptomatic infection, this was not in the context of a single whole-cell vaccine dose. Secondary attack rates arising from pertussis cases among predominantly whole-cell vaccinated children were reported from Senegal in the early 1990s.³ Infectiousness was significantly reduced (−83%; 95% CI, 50% to 93%) in children with clinical pertussis who had received 3 vaccine doses but not among 1-dose vaccinated children (−47%; 95% CI, −128% to 23%). A further consideration is marked variability in the effectiveness of whole-cell vaccines,⁴ limiting generalizability of conclusions.