Quantifying the re-exposure process to an infectious agent
Speaker: Gianpaolo Scalia Tomba, Professor, Department of Mathematics, University of Rome Tor Vergata, Italy.
Gianpaolo Scalia Tomba, Department of Mathematics, University of Rome Tor Vergata, Italy.
For viral infections conferring permanent immunity, re-exposure to the pathogen due to contacts with infectious individuals might be critical for immunity boosting. A major example is represented by the varicella-zoster virus (VZV) where re-exposure is thought to lead to boosting of cell mediated immunity (CMI), which plays a protective role against the development of herpes zoster (HZ). By combining basic concepts from deterministic and stochastic modelling of infection, we develop a basic model for quantifying the potential for re-exposure and immune boosting at any given age. The model is then parametrized using pre-vaccination UK data for measles, mumps and rubella (MMR) and recently collected data on social contacts and serological data for Varicella in Italy. We supply analytical expressions for the expected number of lifetime re-exposures and for underlying age-patterns, including the average age at which the last re-exposure occurs. Based on estimates of the force of (first) VZV infection, we show that the expected number of boosting opportunities of CMI might be in the range 2-3, which is consistent with recent findings about the development of herpes zoster. However, the age at which the last re-exposure to VZV occurs is highly sensitive to the underlying form of the force of infection.
This is joint work with Piero Manfred, Professor, Department of Statistics and Mathematics Applied to Economics, University of Pisa, Italy.