# Modelling the Interplay between Responsive Individual Vaccination Decisions and the Spread of SARS-CoV-2 Open Access

## Wallrafen-Sam, Karina (Spring 2023)

Permanent URL: https://etd.library.emory.edu/concern/etds/5q47rq10c?locale=en
Published

## Abstract

Background. The uptake of primary and booster vaccinations against SARS-CoV-2 infection remains low despite high vaccine effectiveness. Vaccine hesitancy is a major barrier to higher uptake, but it is unclear whether modifying hesitancy could result in substantial prevention benefits. Mathematical models of disease transmission that represent decision-making psychology can provide insight into the potential effects of different interventions against vaccine hesitancy in the context of the ongoing COVID-19 pandemic.

Methods. We coupled a network-based mathematical model of SARS-CoV-2 transmission with a social-psychological vaccination decision-making process in which vaccine side effects and breakthrough (i.e., post-vaccination) infections could "nudge" agents towards vaccine resistance while spikes in COVID-19 hospitalizations could nudge them towards vaccine willingness. This model was parameterized and calibrated to represent the COVID-19 epidemic in the state of Georgia, USA from January 2021 to August 2022. We modelled various intervention scenarios in which increases to the probability of resistant-to-willing attitude switches were combined with decreases to the probability of willing-to-resistant switches. We compared cumulative vaccine doses administered, SARS-CoV-2 incidence, and COVID-related deaths across scenarios.

Results. Increasing the probability that a spike in hospitalized prevalence would prompt vaccine resistant persons to vaccinate and decreasing the probability that breakthrough infections would prompt vaccine willing persons to forgo further vaccination both increased the intermediate outcome of cumulative vaccine doses administered by as much as 1'632.0 doses (50% SI: (1'358.5, 1'854.5)), with the former probability having more of an impact than the latter. However, this additional vaccine coverage built up too slowly to avert a non-negligible number of infections or deaths within our model timeframe. The minimum number of infections across scenarios was 67'111.7 per 100'000 person- years (50% SI: (66'344.0, 67'976.6)), corresponding to only 634.7 (50% SI: (-230.2, 1'402.4)) infections averted per 100'000 person-years.

Conclusions. Reactive interventions may have only a limited ability to avert SARS-CoV-2 infections in the short term. This suggests that attention should be paid to formulating vaccine promotion interventions that anticipate the case curve instead of reacting to it. Our findings also highlight the importance of addressing baseline vaccine unwillingness to reduce the proportion of the population that is entirely vaccine-naïve.

Background. 1

Methods. 3

Results. 9

Discussion. 12

Tables and Figures. 16

References. 34

Appendix. 40