Characteristics of COVID-19 vaccine hesitancy in university students: Methodological insights from a syndemic...

This paper offers a methodological critique of the study by AlShurman et al. that examined whether COVID-19 vaccine hesitancy (VH) and COVID-19-related factors interact to influence booster dose uptake among university students in Canada from a syndemic perspective. The original cross-sectional survey was conducted among 4453 students at the University of Waterloo in 2024. VH was measured retrospectively for primary doses and concurrently for booster doses, with a change score computed to capture shifts in hesitancy over time. Logistic regression models were used to assess the main effects and interactions on additive and multiplicative scales. While the original study provides a valuable application of syndemic theory, notable limitations warrant caution in interpretation. These include substantial recall bias in the retrospective VH change score, the inability of the cross-sectional design to establish temporal dynamics and bidirectional reinforcement required by syndemic theory, low response rate (approximately 11%) raising concerns about selection bias, dichotomization of key variables, untested linearity of the change score, and potential overinterpretation of statistical interactions as mechanistic syndemic synergy. Unmeasured factors such as student stressors, social media exposure, and psychological reactance may also influence the observed associations. The findings should be interpreted conservatively. Targeted interventions such as rebuilding trust and addressing misinformation remain important. However, stronger longitudinal studies with prospective measurement of hesitancy, mediation analyses, and sensitivity testing are needed to more robustly examine syndemic interactions in vaccine uptake.