The syndemic nexus: How vaccine hesitancy and COVID-19 interact to influence vaccine uptake among university students

This study examined whether COVID-19 Vaccine Hesitancy (VH) and COVID-19-related factors interact to influence COVID-19 booster doses uptake among university students in Canada, from a syndemic perspective. A cross-sectional survey was conducted among 4453 students at the University of Waterloo in 2024. VH was measured toward both COVID-19 primary and booster doses. Change in VH scores were computed to capture shifts in hesitancy over time. Logistic regression models assessed the main effects of VH and COVID-19-related factors on booster uptake. Interactions were tested using additive and multiplicative scales. Increased VH was associated with a 23% decrease in booster uptake. Younger ages, not being hospitalized due to COVID-19, not receiving the influenza vaccine, noncompliance with COVID-19 guidelines, and belief in conspiracy theories predicted lower booster uptake. Significant interactions were found between change in VH scores and COVID-19 diagnosis and hospitalization history, guideline adherence, and conspiracy beliefs. For students who did not receive booster doses, the change in VH was greater among those who reported following public health guidance than those who did not. Similarly, for students who did not receive booster doses, the change in VH was greater among those who reported not believing in conspiracy theories compared to those who did. The findings support a syndemic model, indicating that VH and COVID-19-related experiences jointly influence booster uptake. Targeted interventions such as rebuilding trust, addressing misinformation, and reducing stigma may improve booster uptake even if not all barriers are addressed. Further research is needed to examine these interactions.