A Catalytic Model of Infection for Measles

SUMMARY Catalytic epidemic models are concerned with the age distribution at attack of infectious disease. A catalytic linear infection model, in which it is assumed that the force of infection acting on an individual is a linear function of age, is developed and applied to measles. The model is fitted to measles incidence data in England and Wales for the period 1956-69. Trends in time and differences between populations in estimated parameter values are discussed. In particular, it is observed that the (estimated) mean age at attack has decreased linearly with time over that period. It is hypothesized that the introduction of large-scale vaccination programmes may alter the age distribution of attack among the remaining susceptibles.