Estimation of the contact rate in a seasonal SEIR model: application to chickenpox incidence in France

This work was an attempt at analysing the seasonal pattern of varicella epidemics in France by fitting a susceptibles-exposed-infectives-recovered (SEIR) model with a periodic contact rate function to weekly chickenpox incidence data collected over the period 1991 to 1996. The contact rate was assumed to be either a continuous, or a piecewise constant, periodic function. Both assumptions gave a reasonable fit to the data and yielded estimates of the incubation and infectious periods that were consistent with values derived on clinical or serological grounds. Seasonal fluctuation of the estimated contact rate function was likely to reflect the impact of school holidays on chickenpox diffusion among schoolchildren.