In Reply We agree with Snelling and McIntyre that our model, like all models, relies on several assumptions. However, we believe the explicit underlying assumption that an initial dose of the whole-cell pertussis (wP) vaccine followed by the standard course of acellular pertussis vaccination blocks asymptomatic infection is supported by rigorous clinical evidence (studies by Liko et al,¹ Witt et al,² and Sheridan et al,³ as cited in our original study).⁴

They cite Préziosi et al⁵ to argue that 1 dose of wP is not likely to protect against asymptomatic infection because 1 dose did not significantly reduce the secondary attack rate of symptomatically infected individuals.⁵ The study showed that infected individuals who had previously been vaccinated with a single dose of wP transmitted pertussis at the same rate as those who had not been vaccinated. Our model agrees with these findings: symptomatically and asymptomatically infected individuals transmit disease with the same force of infection. In our model, the only difference between acellular pertussis vaccine and wP is that the acellular vaccine allows for asymptomatic infection and wP reduces it.⁴ Because the Préziosi study only examined the effects of vaccination on transmission once infected and not the ability of wP to block infection, it provides little guidance on the ability of the wP to prevent asymptomatic infection.