A Model Basis for the Control of Whooping Cough

The problems of controlling and ultimately eradicating pertussis are addressed in the face of the apparent impermanence of vaccine immunity, and the limited protection offered while it lasts. Interactions between partial immunity, reduced infectiousness, responses to a superimposed natural infection, changing mean ages of infection and alternative rates of transmission before the vaccine was introduced, are considered in an integrated manner. Mathematical expressions were developed for these different components, from which a computer program was constructed for predicting the levels of control to be expected from different vaccination strategies. The most important of the parameters determining outcomes are those relating to levels of uptake, the choice of a one-course or two-course policy, and the specification of the vaccine itself. As might be expected, high levels of uptake and a two-course policy are necessary for high levels of control, but they will not necessarily succeed. The detailed specification of the type of protection to be offered by a vaccine is also crucial. The most important necessity is for a vaccine immunity with a low rate of decay; but in the presence of decay (which greatly reduces the feasibility of eradication) it is important that the vaccine should protect against the clinical disease without preventing the child from being infected with the organism, and thus attaining permanent immunity.