Objective: Evidence suggests young adults in post-secondary school experienced increased distress during the COVID-19 pandemic, but students' experiences likely varied. Effects may have also changed over time as students adapted. This study examined the mental health of students with and without preexisting health conditions at two points during the pandemic (winter 2020/2021 and spring/summer 2021). Methods: Participants (N = 1465) completed a baseline and follow-up questionnaire assessing their health history, depressive symptoms, anxiety symptoms, stress, and COVID-19-related worry and perceived vulnerability of severe infection. Results: At both time points, students with preexisting health conditions reported greater distress than those without preexisting health conditions. Stress increased from time 1 to time 2 for all students, and participants with preexisting health conditions significantly increased in their COVID-19 perceived vulnerability of severe infection over time. Conclusions: Findings highlight the need for additional and ongoing mental health supports for vulnerable students throughout the pandemic.