The Cultural Evolution of Vaccine Hesitancy: Modeling the Interaction between Beliefs and Behaviors

Abstract

In the last decade, despite the proven efficacy of vaccines, the developed world has seen a resurgence of vaccine-preventable diseases (VPDs) such as measles, pertussis, and polio. Vaccine hesitancy, an individual behavior influenced by historical, political, and socio-cultural factors, is believed to be a primary factor responsible for decreasing vaccine coverage, thereby increasing the risk and occurrence of VPD outbreaks. Society, culture, and individual motivations affect human decisions regarding health behavior and preventative care, and health perceptions and health-related behaviors can change at the population level as cultures evolve. In recent years, mathematical models of disease dynamics have begun to incorporate aspects of human behavior, however they do not address how evolving cultures influence these health behaviors. Here, using a mathematical modeling framework, we explore the effects of cultural evolution on vaccine hesitancy and vaccination behavior. With this model, we shed light on the facets of cultural evolution (vertical and oblique transmission, homophily, etc.) that promote the spread of vaccine hesitancy, ultimately affecting levels of vaccination coverage and VPD outbreak risk in a population. In addition, we present our model as a generalizable framework for exploring cultural evolution when beliefs influence, but do not strictly dictate, human behaviors. We show vaccine confidence and vaccine-conferred benefits can be driving forces of vaccine coverage, and we demonstrate that an assortative preference among vaccine-hesitant individuals can lead to increased vaccine hesitancy and lower vaccine coverage. Further, we show that vaccine mandates can lead to a phenomenon in which high vaccine hesitancy co-occurs with high vaccination coverage, and that high vaccine confidence can be maintained even in areas where access to vaccines is limited.

Internal and external factors affecting vaccination coverage: modeling the interactions between vaccine hesitancy, accessibility, and mandates

“…Here, we build on the cultural niche construction framework proposed by [26] to model the cultural spread of vaccine attitudes and vaccination behavior in the presence of external forces imposed by two scenarios: vaccine mandates and vaccine inaccessibility. Multiple factors influence an individual's vaccine-related beliefs and a couple's decision to vaccinate their offspring, including their own vaccination status and their perception of the relative risks of the disease and the vaccine.…”

“…With our initial model [26], we showed that when population traits are at or near an equilibrium, we can infer that a population with high vaccination coverage will have low rates of vaccine hesitancy and vice versa. However, when there are external pressures as modeled here, such as increased pressure to vaccinate or difficulty in acquiring vaccination exemptions, an undercurrent of vaccine hesitancy can persist in a relatively well-vaccinated population, potentially limiting the adoption of newly introduced vaccines.…”

“…We build on a more general cultural niche construction framework of [24,26] to assess the effects of vaccine mandates and vaccine accessibility on the resulting landscape of vaccination coverage and vaccine confidence. For a population of individuals, we track the status of vaccination coverage and vaccine confidence over time; within this population, individuals mate, decide whether to vaccinate their offspring, and transmit a vaccine attitude trait.…”

“…The simulation is run until phenotype frequencies reach equilibrium ( Figure 1, Table 1 ). For more detail see Supplemental Text S1 and [26]. All code to run the simulations is provided at www.github.com/CreanzaLab/VaccineModel.…”

“…We adapted a cultural niche construction framework to model vaccination beliefs and behaviors, incorporating the transmission of vaccine culture both from parents and from the community [26]. Using this model, we previously demonstrated that the overarching cultural landscape, including the likelihood of adopting vaccine hesitancy and the probability of transmitting it to one's children, determines the equilibrium levels of vaccination coverage and vaccine hesitancy in a population.…”