Microbial evolution (Communication arising): Antitoxin vaccines and pathogen virulence

Soubeyrand and Plotkin question our contention that antitoxin vaccines may select for greater pathogen virulence, arguing that this has not been borne out in real-life cases of diphtheria and pertussis, in which the widespread use of antitoxin vaccines has led to a reduced incidence of severe disease. They explain this success in terms of direct effects by the toxin on transmission that are both beneficial and costly. They argue that antitoxin vaccines have relieved the pathogen of the cost of high virulence due to host mortality (as we do too), but that these vaccines also maintain the metabolic cost of producing the toxin, helping natural selection to weed out the toxin producers.