operator(3) Varicella zoster virus.(3) Infectious disease(3) Time-varying frailty.(3) Bayesian melding(3) Eigenfunction(3) Contact data(3) social contact(3) Italy(3) Time use data(3) Eigenvalue(3) parvovirus B19(3) Bayesian inference(1) Time-varying parameters.(1) Particle MCMC(1) Population epidemic model(1)