New Model of Public Health Value of Vaccination Integrating Social Network Structure and Time-Varying Parameters. We introduce a new mathematical model of public health value of vaccination that integrates social network structure and time-varying parameter into a traditional model, the SEIR model. Traditional epidemiological models tend to assume homogeneity of the population and constant parameters for all health-relevant measurements such as transmission rates and vaccine efficacy. However, in practical contexts, the contact rates between individual and population and the epidemiology of transmission of the disease vary extensively among different social groups and over time.