We have been studying compartmental models of infectious disease spread, considering voluntary vaccination. The law governing the dynamics of voluntary vaccination is defined such that each individual chooses whether or not to be vaccinated, influenced by their perception of the choices of other individuals and the state of the disease in the system. This is known in the literature as imitation dynamics. I will present a simple model that explains the main ideas behind the construction of this type of model. The use of imitation dynamics in this model led to the emergence of chaotic behavior. I will also present two other models, one with an age structure and the other with loss of immunity.