The force of measles infection in East Africa.

Catalytic models were applied to age-specific incidence data from two East African studies in order to study the force of measles infection in relation to age. The results are compared with the pattern observed in England and Wales. In East Africa the force of measles infection appears to be independent of age, probably as a result of sociocultural factors. Consequently the incidence of measles is highest in the second half of the first year of life and decreases with increasing age. Major vaccination efforts will raise the average age of measles attack, but the peak incidence will remain in the first year of life. This complicates the decision on the optimal age for vaccination and the need for incidence surveillance is stressed. The simple catalytic model, which is based on the assumption of an age-independent force of infection may play an important role in measles surveillance. With this model simple and economic surveillance studies could be designed which use cross-sectional data only.