THE DYNAMICS OF SMALLPOX EPIDEMICS IN BRITAIN, 1550-1800

Time-series analysis, a valuable tool in studying population dynamics, has been used to determine the periodicity of smallpox epidemics duri ng the seventeenth and eighteenth centuries in two contrasting represe ntative situations: 1) London, a large city where smallpox was endemic , and 2) Penrith, a small rural town. The interepidemic period was fou nd to be two years in London and five years in Penrith. Equations gove rning the dynamics of epidemics predict 1) a two-year periodicity and 2) that oscillatory epidemics die out quickly. It is suggested that ep idemics were maintained by a periodic variation in susceptibility link ed either to a five-year cycle of malnutrition or to an annual cycle. Computer modeling shows how the very different patterns of epidemics a re related to population size and to the magnitude of the oscillation in susceptibility.