Vaccine hesitancy predicts future COVID-19 vaccine side effects
While the production of COVID vaccines could have been the “light at the end of the pandemic tunnel,” this outcome was hampered at critical stages by vaccine hesitancy, defined by the World Health Organization (WHO) as “the reluctance or refusal to vaccinate despite the availability of vaccines.”
The precise relationship between vaccine hesitancy and COVID-19 vaccination side effects has not previously been explored in vaccinated persons. A fundamental question arises in regard to the directionality of this vaccine hesitancy-vaccine side effect link, namely which variable predicts which. One possibility is that side effects from an earlier dose predict one’s vaccine hesitancy towards a later dose. Alternatively, one’s psychological negativity (hesitancy) towards an earlier dose could predict subsequent side effects from a later vaccination dose. The latter direction reflects a Nocebo effect, i.e., side effects driven by psychological factors rather than by an active treatment component.
The unique, contiguous waves of COVID-19 vaccinations have presented an opportunity to test the nocebo effect on vaccinated individuals. In a new study, researchers from Bar-Ilan University and Ariel University in Israel examined this issue in 750 older adults. Older adults are advantageous as they have a high vaccination rate coupled with low side effects, rendering detection of such nocebo effects more challenging. To address this issue, one needs to assess both variables (vaccine hesitancy and side effects) at two different time points (after the second vaccination dose and six months later after the booster dose) and examine if wave-1 side effects predict wave-2 hesitancy, or whether wave-1 hesitancy predicts w2side-effects. This design is very conservative, and the statistical threshold for such effects is conceptually high, as such effects have to hold beyond all other effects. Results showed only the latter direction to be true. Namely, only earlier vaccine hesitancy towards the second COVID-19 dose predicted subsequent nocebo side-effects following the booster vaccination. To put this in perspective up to 16% of one’s vaccine side effects were explained by earlier vaccine hesitancy. Supplementary analyses revealed that results held beyond specific side effects and vaccine-hesitancy items.
Typical of nocebo effects, compatible gender differences were observed. For example, the nocebo effect in females is more impacted by previous experience. Following, the link between previous side effects and current side effects, was twice as large in females versus males.
