Background <p>Contact tracing is an important tool in slowing the spread of infectious disease and preventing illness. People may face barriers to contact tracing adherence, depending on various personal and contextual characteristics. Thus, we examined a large-scale COVID-19 contact tracing initiative and compared adherence across several socio-demographic and exposure characteristics.</p> Methods <p>We analyzed data for 130,255 participants in Ontario’s COVID-19 contact tracing initiative from September 2020 to December 2021. During contact follow-up calls, callers recorded whether contacts reported self-isolating and whether they completed follow-up. We performed unadjusted and adjusted logistic regressions to estimate the odds ratios (OR) and 95% confidence intervals (CI) of self-isolating and of completing follow-up, according to contacts’ age group, neighbourhood material resources, COVID-19 wave, exposure setting, region, and preferred language.</p> Results <p>In the adjusted analyses, odds of completing follow-up decreased as neighbourhood-level material resources decreased, with OR = 0.57 (95% CI: 0.54–0.60) comparing highest resource areas to lowest. Compared to COVID-19 contacts living in the Greater Toronto Area, other Ontario regions had higher odds of completing follow-up, with ORs ranging from 1.19 (95% CI: 1.14–1.24) to OR = 1.91 (95% CI: 1.78–2.04). Contacts whose preferred languages were not English had lower odds of self-isolating (OR = 0.57, 95% CI: 0.38–0.84). The 0–4 and 5–11 year old age groups had lower odds of self-isolating than 20–29 year olds, with respective ORs of 0.60 (95% CI: 0.48–0.75) and 0.57 (95% CI: 0.48–0.67).</p> Conclusions <p>In preparing for future pandemics, contact tracing programs may benefit from prioritizing additional supports for those who live in areas with fewer material resources, have language preferences other than English, and live in large metropolitan centres.</p>