Predicting the side effects of influenza vaccination.

Background: Side effects following vaccination intensify vaccine hesitancy, which remains a significant challenge to public health. Research suggests that a proportion of side effects are not caused by the vaccine but are instead associated with psychological factors that influence nocebo responding.

Purpose: This study investigates the psychological and demographic factors associated with symptom reporting postvaccination, the attribution of these symptoms as side effects, and their influence on future intentions to vaccinate.

Methods: A prospective, longitudinal design was employed with 225 influenza vaccination recipients. Demographic and psychological measures (including anxiety, vaccination attitudes, and side effect expectations) were completed at baseline. Side effects were measured immediately and 1-week following the vaccination. Future intentions to vaccinate were measured 1-week postvaccination.

Results: Anxiety (P < .001) and perceived sensitivity to vaccines (P = .044) predicted the number of symptoms reported immediately following vaccination. Anxiety (P < .001) and perceived sensitivity (P = .035) along with baseline symptoms (P < .001) predicted symptoms 1 week following the vaccination. Female gender (P = .003), younger age (P = .018), anxiety (P < .001), and baseline symptoms (P = .009) predicted whether participants attributed symptoms as vaccination side effects. Anti-vaccination attitudes were associated with less intention to vaccinate in the future (P = .033).

Conclusions: Nocebo-associated psychological factors contributed to symptoms experienced after an influenza vaccination. Findings demonstrate that the way symptoms are noticed, and then interpreted as side effects, appear to be separate mechanisms promoted by different factors. This study improves identification of side effect reporters prior to vaccination.