An Exploration of Implementing Herd Immunity Into Static Models for Economic Evaluation of Vaccines
Author(s)
Josie Dodd, BSc, MSc, PhD, Des Dillon-Murphy, BSc, MSc, PhD, Ruth Chapman, BA, MSc, PhD.
PPD Evidera Health Economics & Market Access/Thermo Fisher Scientific, London, United Kingdom.
PPD Evidera Health Economics & Market Access/Thermo Fisher Scientific, London, United Kingdom.
OBJECTIVES: Static models are widely used in health economics to evaluate the impact vaccination programs. However, these models are inherently conservative as they do not intrinsically account for herd immunity, which can significantly amplify the benefits of vaccination. There are many examples of static cost-effectiveness models that include a herd immunity to attempt to capture the full benefit of the vaccination in a simplified manner. This study aims to explore methods for incorporating rate-dependent herd immunity into static models.
METHODS: We developed both a Dynamic Transmission Model (DTM) and an equivalent static model for a hypothetical infectious disease. We compared the total number of infections predicted by the DTM under each vaccination strategy, analysing the differences in infection rates to determine the relationship between vaccination rollout strategies and herd immunity. Functions that approximate herd immunity effect were incorporated into the static model. Finally, we compared the adjusted static model outcomes with the original DTM outcomes to analyse how different approaches compare to a dynamic model representation of indirect effects. The impact of altering vaccine coverage, rollout speed, and incorporating different levels of complexity in the model on predicted herd immunity is also examined, aiming to provide recommendations on including herd immunity in a static model.
RESULTS: This work serves as a proof of concept that allows us to robustly evaluate the effects of herd immunity based on rate of vaccine rollout in a static model. The proposed methods investigate herd immunity as a function of vaccine rollout, highlighting key considerations required to accurately capture indirect effects.
CONCLUSIONS: Incorporating herd immunity into static models offers a practical and effective way to enhance the economic evaluation of vaccine programs. This investigation provides a framework for including indirect effects in static models, which could be leveraged in HTA/NITAG assessments.
METHODS: We developed both a Dynamic Transmission Model (DTM) and an equivalent static model for a hypothetical infectious disease. We compared the total number of infections predicted by the DTM under each vaccination strategy, analysing the differences in infection rates to determine the relationship between vaccination rollout strategies and herd immunity. Functions that approximate herd immunity effect were incorporated into the static model. Finally, we compared the adjusted static model outcomes with the original DTM outcomes to analyse how different approaches compare to a dynamic model representation of indirect effects. The impact of altering vaccine coverage, rollout speed, and incorporating different levels of complexity in the model on predicted herd immunity is also examined, aiming to provide recommendations on including herd immunity in a static model.
RESULTS: This work serves as a proof of concept that allows us to robustly evaluate the effects of herd immunity based on rate of vaccine rollout in a static model. The proposed methods investigate herd immunity as a function of vaccine rollout, highlighting key considerations required to accurately capture indirect effects.
CONCLUSIONS: Incorporating herd immunity into static models offers a practical and effective way to enhance the economic evaluation of vaccine programs. This investigation provides a framework for including indirect effects in static models, which could be leveraged in HTA/NITAG assessments.
Conference/Value in Health Info
2025-11, ISPOR Europe 2025, Glasgow, Scotland
Value in Health, Volume 28, Issue S2
Code
PT30
Topic
Epidemiology & Public Health, Health Technology Assessment, Methodological & Statistical Research
Disease
Vaccines