A Syndemic Approach to Understanding and Exploring COVID-19 Vaccine Hesitancy among University of Waterloo Students, Canada

Abstract

Vaccine hesitancy (VH) remains a persistent challenge to achieving widespread COVID-19 vaccination. Although initial vaccine rollout efforts witnessed high uptake of the primary series, booster dose uptake has declined, particularly among younger adults. Universities, where primary doses were mandated but boosters remained optional, offer a unique setting to study VH dynamics. These institutions encompass socially connected, information-exposed populations who navigate a developmental stage for forming health-related decisions.

Recent scholarship has conceptualized VH not only as an individual behavioral issue but as a social phenomenon that spreads across communities, often amplified by misinformation and peer influence. Given that COVID-19 has been described as a biological pandemic and VH as a social epidemic, their co-occurrence may constitute a syndemic, where each amplifies the effects of the other and suppresses vaccine uptake. As booster coverage continues to decline, applying a syndemic lens to VH among students is essential for guiding future vaccination strategies.

This dissertation addresses critical gaps in COVID-19 VH research. First, existing scales offered limited constructs that did not capture the multidimensional nature of VH or were not validated for booster-specific attitudes. Additionally, most prior studies assessed VH at a single vaccine stage, overlooking how attitudes evolve from mandatory primary series to voluntary booster decisions. Moreover, while syndemic theory has gained traction conceptually, its empirical application in the context of VH remains limited, with most studies relying on theoretical or qualitative descriptions rather than quantitative tests of interaction effects. To address these gaps, the objectives of this thesis were to (1) validate a COVID-19 Vaccine Hesitancy Scale (CVHS) to measure VH for COVID-19 primary and booster doses among students at the University of Waterloo (UW) in Canada, (2) estimate COVID-19 VH prevalence and identify key factors driving VH across primary and booster doses, and (3) examine the syndemic interaction between VH and COVID-19-related factors (e.g., COVID-19 diagnosis, COVID-19 hospitalization, adherence to public health guidelines, and beliefs in conspiracy theories) in shaping booster uptake.

This dissertation is based on a cross-sectional survey of 4,453 students at UW, Canada, conducted in 2024. The first study adapted the CVHS to measure VH toward both primary and booster COVID-19 doses among university students. Exploratory and confirmatory factor analyses, along with reliability and validity tests, were conducted to assess the underlying factor structure and evaluate model fit. Results indicated a three-factor structure across both scales, with high internal consistency and excellent model fit. The scale demonstrated adequate convergent, discriminant, and criterion validity. VH was significantly higher for booster doses (33.4%) than primary doses (19.3%) with more students delaying (32.1%) or refusing boosters (29.3%) than delaying (11.5%) or refusing (6.2%) primary doses.

The second study examined how VH shifted from primary to booster doses and what factors contributed to this VH change using Generalized Estimating Equations. Results showed a marked increase in VH, with mean scores rising from 7.3 (SD = 7.1) for primary doses to 10.9 (SD = 8.1) for boosters. VH prevalence doubled from 17% to 33.4%. The largest VH increases were seen among women and younger students. Students with low perceived risk, negative booster perceptions, low trust in government recommendations, and lack of prior flu or meningococcal vaccination showed greater VH change. Conversely, students with no religious affiliation and those less influenced by vaccine mandates showed smaller VH shifts.

The third study tested the central syndemic hypothesis and investigated whether changes in VH interacted with COVID-19-related experiences to influence booster dose uptake. Logistic regression models were used to estimate main and interaction effects on booster uptake. Increased VH was associated with a 23% reduction in the likelihood of receiving a booster. Younger age, no COVID-19 hospitalization, absence of flu vaccination, non-compliance with public health guidelines, and belief in conspiracy theories predicted lower booster uptake. Interaction analyses revealed that the negative effect of VH on booster uptake was stronger among students who complied with public health guidelines and those who rejected conspiracy beliefs. Interestingly, among participants uncertain about their hospitalization status, increased VH was associated with higher booster uptake.

This dissertation contributes new evidence that VH is dynamic and context-dependent, evolving significantly between vaccine phases. Findings underscore that the effect of VH is magnified when interacted with COVID-19 experiences such as pandemic fatigue, stigma, and conspiracy beliefs, together constituting a syndemic. This indicates the presence of a “latent hesitancy” among individuals who may outwardly engage in preventive behaviors but internally remain skeptical or fatigued by ongoing vaccine messaging. As such, vaccine mandates, broad awareness campaigns, or generic messaging may be insufficient to address the complex drivers of booster hesitancy. Instead, interventions should be segmented and tailored to specific behavioral profiles, such as compliant-but-hesitant versus disengaged-and-distrustful, rather than treating students as a homogeneous group. Strategies should go beyond one-size-fits-all models and adopt dialogic and supportive approaches, such as vaccine counseling sessions, peer-led discussions, or transparent communication from trusted campus figures. Furthermore, institutions should recognize that VH may shift over time. Ongoing monitoring of VH levels and underlying factors through rapid surveys can support targeted public health interventions.