Epidemiological evidence for herd immunity induced by acellular pertussis vaccines

In a series of elegant experiments on baboons, Warfel et al. conclude that acellular pertussis vaccines (aP) prevent disease but fail to protect against transmissible infection (1). The authors speculate that this fact may explain the resurgence of pertussis in some countries (2). Although the animal model of Warfel et al. is a true breakthrough, we question the soundness of their extrapolation to transmission in human populations. Indeed, much available epidemiological evidence argues against it. The precise nature of vaccine-induced protection is both controversial and consequential. Vaccines that protect against transmissible infection protect those vaccinated directly, but also protect the unvaccinated who benefit from decreased infection risk: so-called herd immunity. In contrast, vaccines that protect against disease but not transmission benefit only the vaccinated. Although experimental evidence on the transmission impacts of pertussis vaccination is …