Simulation of measles epidemics, behaviour of parameter estimates for different models of vaccine action

by Dupuis, Michelle Annie.

Using epidemic simulations in randomly mixing and stratified populations un- der different rnodels of vaccine action, the best estimator of vaccine efficacy for each model is identified. For the type 1 and general vaccine models, vaccine efficacy is best calculated from incidence densi ty rates or transmission rates. In large epidemics, these estimates may underestimate the true vaccine efficacy. For the type iI model, estimates based on relative attack rates are preferable. Assuming an incorrect model of vaccine action will result in estimates which decrease or increase over time. Individuals who are immune £rom having previously contracted the disease should be excluded from the study if the vaccine is a type 1 or general vaccine, whereas they should not be excluded if the vaccine is a type II vaccine. Some of the complicating issues encountered in real outbreak situations are discussed using data from a measles outbreak in Muyinga, Burundi.