Dynamics of psychological distress: understanding the impact of intraindividual and interindividual factors in the Belgian population during the COVID-19 pandemic-a multilevel prospective cohort study.

Introduction: Longitudinal studies have identified an increase in psychological distress throughout the general population during the COVID-19 pandemic. Nevertheless, the determinants of the variation in psychological distress are unclear. This paper investigated factors that were likely to be associated with psychological distress variation: exposure to COVID-19 and psychosocial factors. Methods: Five waves of a prospective cohort survey were conducted with a convenience sample of the general population in Belgium between March 2020 and November 2021 (n=4,550). Psychological distress was measured using the GHQ-12. Two groups of exposures were investigated: self-reported exposure to COVID-19 and psychosocial factors (loneliness, social support, and social activities). We first partitioned the variance into an interindividual component (time-invariant) and an intraindividual component (time-variant). Linear mixed models were used for analysis. Results: Most of the variance in psychological distress was interindividual. For both sources of variance (interindividual and intraindividual), the change in psychological distress was mainly associated with psychosocial factors, rather than pandemic-related factors. Loneliness emerged as the factor most strongly associated both with interindividual and intraindividual differences in psychological distress. Discussion: Overall, these findings suggest that the variation in psychological distress between the waves was mostly influenced by social support, loneliness, and social activities, rather than by exposure to COVID-19. Mitigation policies aimed at controlling the pandemic should focus more on addressing specific individual psychosocial vulnerabilities.