title: Estimating the age-specific duration of herpes zoster vaccine protection: a matter of model choice?
abstract: BACKGROUND
  The estimation of herpes zoster (HZ) vaccine efficacy by time since vaccination and age at vaccination is crucial to assess the effectiveness and cost-effectiveness of HZ vaccination. Published estimates for the duration of protection from the vaccine diverge substantially, although based on data from the same trial for a follow-up period of 5 years. Different models were used to obtain these estimates, but it is unclear which of these models is most appropriate (if any). Only one study estimated vaccine efficacy by age at vaccination and time since vaccination combined. Recently, data became available from the same trial for a follow-up period of 7 years.
  
  
  OBJECTIVE
  We aim to elaborate on estimating HZ vaccine efficacy (1) by estimating it as a function of time since vaccination and age at vaccination, (2) by comparing the fits of a range of models, and (3) by fitting these models on data for a follow-up period of 5 and 7 years.
  
  
  RESULTS
  Although the models' fit to data are very comparable, they differ substantially in how they estimate vaccine efficacy to change as a function of time since vaccination and age at vaccination.
  
  
  CONCLUSIONS
  An accurate estimation of HZ vaccine efficacy by time since vaccination and age at vaccination is hampered by the lack of insight in the biological processes underlying HZ vaccine protection, and by the fact that such data are currently not available in sufficient detail. Uncertainty about the choice of model to estimate this important parameter should be acknowledged in cost-effectiveness analyses.
authors.affiliation: Center for Health Economic Research and Modeling Infectious Diseases (CHERMID), Vaccine and Infectious Disease Institute (Vaxinfectio), University of Antwerp, Universiteitsplein 1, Wilrijk, Belgium. joke.bilcke@ua.ac.be
authors.forename: Joke
authors.initials: J
authors.lastname: Bilcke
authors.forename: Benson
authors.initials: B
authors.lastname: Ogunjimi
authors.forename: Frank
authors.initials: F
authors.lastname: Hulstaert
authors.forename: Pierre
authors.initials: P
authors.lastname: Van Damme
authors.forename: Niel
authors.initials: N
authors.lastname: Hens
authors.forename: Philippe
authors.initials: P
authors.lastname: Beutels
mesh_terms: D000367:Age Factors; D006562:Herpes Zoster / Q000517:prevention & control*; D053061:Herpes Zoster Vaccine / Q000276:immunology; D006801:Humans; D015233:Models, Statistical; D013997:Time Factors
chemical_list: D053061:Herpes Zoster Vaccine