The effect of herd immunity thresholds on willingness to vaccinate against COVID-19

Abstract

Since the early days of the COVID-19 pandemic, media and policy makers have speculated about herd immunity and the threshold for numbers of immune citizens needed for reaching it. What are the effects of such numerical goals on willingness to vaccinate? In a large representative sample of unvaccinated Swedes we find that giving a low (60%) compared to a high (90%) threshold have direct effects on beliefs about reaching herd immunity and beliefs about how many others will get vaccinated. Presenting the high threshold makes people believe that herd immunity is harder to reach, compared to the low threshold, yet at the same time people also believe that a higher number of the population will get vaccinated. Since these beliefs affects willingness to vaccinate in opposite directions, some individuals are encouraged and others discouraged depending on the threshold presented. This has consequences for ongoing COVID-19 vaccination and future vaccination campaigns