The long term goal of this work is to develop a systematic, dynamic demographic framework within which to analyze individual-level and population-level morbidity and mortality patterns stemming from infectious diseases. This proposed research aims to characterize epidemiologic and demographic mechanisms underlying temporal variability in morbidity and mortality caused by aerogenically transmitted pediatric infectious diseases in humans. The specific objectives of this project are to: 1. Identify patterns of age-specificity in contact and transmission which can drive cycles in age-structured epidemic models; 2. Extend methods of formal demography to develop and apply computational formulae for period and amplitude of cycles in disease level generated by such age-specificity; 3. Study the effects of seasonality and stochastic perturbations on the characteristics of cyclical variation in disease prevalence. A major outcome of the proposed work will be the identification of quantitative and qualitative criteria to distinguish the consequences of different mechanisms underlying cyclicity. These criteria could yield broad guidelines for the possible consequences of vaccination schedules under a range of contact rate specifications. A combination of formal dynamical analysis and simulation studies will be used to achieve these aims. These objectives will be supported by concurrent but separate work on the development of data-analytic criteria and methodology for the analysis of MDC and LDC data sets.