Impact on immunization of seasonal cycle of chickenpox.

The objective of this work was to study the effect of incorporating a seasonal term in a compartmental age-structured theoretical transmission model, on the performance of vaccination strategies for chickenpox. The epidemiologic parameters are taken from data or are based on a review of literature. We used a realistic age-structure model (RAS): It is a model that incorporate both age and seasonal structure. The seasonality was introduced in the model with the addition of sinusoidal forcing term. This seasonal term varies between 0 and 1. From a susceptible/exposed/infectious/removed (SEIR) model with or without age-structure, the pattern of time series is dramatically modified after introducing a seasonal term. This dynamic ends to the transition to chaos. Regarding the evaluation of vaccination strategies, the results of the model without seasonality may be disturbed when the seasonality is introduced, especially during the first 30 years of simulations.