Dynamics of depressive states among university students in Japan during the COVID-19 pandemic: an interrupted time series analysis

BACKGROUND: The coronavirus disease 2019 (COVID-19) pandemic was reported to have increased depression among university students which was associated with impairments in their campus lives. This study examined changes in depressive states among Japanese university students during the COVID-19 pandemic. METHODS: A secondary data analysis from a factorial randomized controlled trial involving smartphone-based cognitive-behavioral therapy was performed. Six cohorts (N = 1626) underwent an 8-week intervention during the spring or autumn of 2019–2021, with a 9-month follow-up. We evaluated participants’ depressive states weekly using the Patient Health Questionnaire-9 (PHQ-9) during the intervention, with monthly evaluations thereafter. The follow-up periods included Japan’s four states of emergency (SOEs) to control COVID-19. Hypothesizing that SOEs caused a sudden worsening of depressive states, Study 1 compared the cohorts’ PHQ-9 scores, and Study 2 employed time series analysis with a mixed-effects model to estimate identified changes in PHQ-9 scores. RESULTS: Although no changes in depressive states were observed in relation to the SOEs, Study 1 identified sudden increases in PHQ-9 scores at the 28-week evaluation point, which corresponded to the beginning of the new academic year for the three autumn cohorts. In contrast, the three spring cohorts did not exhibit similar changes. Study 2 showed that, for all three autumn cohorts (n = 522), the 0.60-point change was significant (95% CI 0.42–0.78; p < .001) at 28 weeks; that is, when their timeline was interrupted. CONCLUSIONS: While the results do not indicate any notable impact of the SOEs, they highlight the influence of the new academic year on university students’ mental health during COVID-19. Trial registration UMIN, CTR-000031307. Registered on February 14, 2018. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1186/s12991-023-00468-9.