THE DYNAMICS OF MEASLES EPIDEMICS

The interepidemic interval (T) of measles in London from 1647 to 1837 evolved progressively from 5-yearly to 2-yearly by 1800. Measles morta lity was significantly (p < 0.001) cross-correlated with the annual wh eat prices, a good index of nutrition although at a P-year lag. Epidem ics correlated with low autumn temperatures (p < 0.001). A linearised model of the dynamics of epidemics shows that T is determined by the p roduct of population (N) and susceptibility (beta) and that the system will settle at its steady state unless the epidemics are driven. It i s suggested that (i) the progressive change in T was caused by a rise in population size (N) and an increased susceptibility (beta) related to malnutrition and (ii) epidemics were driven by oscillations in low autumn temperature (p < 0.001) and by cycles of susceptible young chil dren produced by malnutrition during pregnancy. (C) 1997 Academic Pres s.