Structured health behavior and epidemic control

Abbas K. Rizi (DSc), Postdoctoral Researcher, DTU Compute, Denmark

Spread and control of infectious diseases depend not just on the biology of a pathogen but on the social fabric of its host population. How people interact and whether their health behaviors cluster along social lines shape how outbreaks unfold and how effectively they can be contained. A vaccination campaign that succeeds in one population may fall short in another simply because the social structure is different. In this talk, I first show how social network structure shapes epidemic trajectories and intervention effectiveness. Taking vaccination as a central example, I demonstrate how herd immunity becomes harder to achieve when vaccinated individuals mix assortatively and cluster, because clustering allows pockets of susceptibility to persist even at high average coverage. I then present an empirical picture from Denmark during COVID-19. Using linked national testing, vaccination, and registry data, we document pronounced clustering in testing uptake and vaccine acceptance, structured by age, geography, socioeconomic status, and personality. This heterogeneity biases inference under standard well-mixed models, distorts herd immunity assessments, and shifts the relative effectiveness of interventions. Health behavior is a structured social response, not a uniform population parameter, and accounting for this has direct consequences for equity-aware public health policy.