Modeling the effects of varicella vaccination programs on the incidence of chickenpox and

Two possible dangers of an extensive varicella vaccination program are more vari-cella (chickenpox) cases in adults, when the complication rates are higher, and an increase in cases of zoster (shingles). Here an age-structured epidemiologic–demo-graphic model with vaccination is developed for varicella and zoster. Parameters are estimated from epidemiological data. This mathematical and computer simu-lation model is used to evaluate the effects of varicella vaccination programs. Al-though the age distribution of varicella cases does shift in the simulations, this does not seem to be a danger because many of the adult cases occur after vaccine-induced immunity wanes, so they are mild varicella cases with fewer complications. In the simulations, zoster incidence increases in the first three decades after initiation of a vaccination program, because people who had varicella in childhood age without boosting, but then it decreases. Thus the simulations validate the second danger of more zoster cases. c © 1999 Society for Mathematical Biology 1