The epidemiology of herpes zoster after varicella Immunization under different biological hypotheses: perspectives from mathematical modeling

The impact of varicella vaccination on the epidemiology of herpes zoster (HZ) critically depends on the mecha- nism of immunological boosting, through which reexposures to varicella-zoster virus are thought to reduce the in- dividual risk of HZ development. However, the qualitative and quantitative dynamics of this process are largely unknown. Consequently, mathematical models evaluating immunization strategies need to rely on theoretical as- sumptions. Available varicella-zoster virus models can be classified in 3 main families according to the postulated effect of exogenous boosting: 1) progressive accumulation of immunity following repeated reexposures; 2) partial protection that wanes over time; or 3) full but temporary immunity against HZ. In this work, we review and compare quantitative predictions from the 3 modeling approaches regarding the effect of varicella immunization on HZ. All models predict a qualitatively similar, but quantitatively heterogeneous, transient increase of HZ incidence. Our results reinforce the idea that a better understanding of HZ pathogenesis is required before further mass varicella immunization programs are set out.