Course of well-being and mental health in Switzerland during the COVID-19 pandemic: results of a national survey within the framework of the COH-FIT study.

Introduction: The COVID-19 pandemic significantly impacted the mental health of the Swiss population. Methods: This study analyzed data from the Collaborative Outcome study on Health and Functioning during Infection Times (COH-FIT) across three pandemic waves: T1 (April-June 2020), T2 (July-December 2020) or T3 (January-June 2021). Each participant participated only once, during one of these three waves. Participants reported their subjective well-being and mental health status for the two weeks prior to the pandemic (pre-pandemic baseline) and during their respective pandemic wave. Subjective well-being was assessed using the World Health Organization Well-Being Index (WHO-5) from 4,037 participants, while mental health was measured via the P-score, completed by 3,375 participants. The WHO-5 ranges from 0 to 100, with higher scores indicating better well-being, while the P-score also ranges from 0 to 100 whereas higher scores represent greater levels of perceived burden across five domains of mental health. Pre- and intra-pandemic differences were analyzed using Wilcoxon tests and ANOVA, with subgroup analyses across seven Swiss regions utilizing the Kruskal-Wallis test. Results: Participants had a mean age of 45.6 years (61.9% female). Results showed a substantial decline in well-being during the pandemic, with average WHO-5 scores decreasing from 75.3 pre-pandemic, to 66.5 during the first wave, 69.1 during the second, and 65.1 during the third, representing relative reductions of 11.7%, 8.2%, and 13.5%. The percentage of participants at risk for depression (WHO-5 <50) peaked during the third wave at 19.8%, up from 10.0% pre-pandemic. Mental health burden, as measured by the P-score, increased significantly during the first wave (from 20.6 to 27.3, +32.5%), and remained elevated across the two subsequent waves, with no significant recovery observed. Wilcoxon tests indicated significant differences between pre-pandemic and intra-pandemic WHO-5 and P-scores, with the largest effect sizes during the third wave ( Discussion: Overall, these findings highlight the considerable and lasting impact of COVID-19 on mental health in Switzerland, emphasizing the need for targeted interventions, particularly in the most affected regions.