Objectives.It has been shown that psychological distress rose rapidly as the COVID-19pandemic emerged and then recovered to pre-crisis levels as social lockdown restrictionswere eased in the United States. The aim of the current study was to investigatepsychosocial and behavioural factors that may explain the rise and fall of distress duringthe initial months of the COVID-19 crisis.Design.This study examined six waves of longitudinal nationally representative datafrom the Understanding America Study (UAS) collected between March and June 2020(N=7,138, observations=34,125).Methods.Mediation analysis was used to identify whether changes in distress (PHQ-4)during the COVID-19 pandemic were explained by the following factors: perceivedinfection risk and risk of death, perceived financial risks, lifestyle changes resulting fromthe virus, perceived discrimination related to the virus, and changes in substance use andemployment status.Results.All mediating factors played a role in explaining changes in distress and togetheraccounted for 70% of the increase in distress between 10-18 March and 1-14 April and46.4% of the decline in distress between 1-14 April and early June 2020. Changes inperceived health risks were most important in explaining changes in distress followed bychanges in lifestyle and the perceived financial risks associated with COVID-19.Conclusions.This study provides longitudinal population-based evidence detailing themediating factors explaining changes in distress during the COVID-19 crisis. Perceivedhealth risks associated with the virus may play a key role in explaining rising and fallinglevels of psychological distress during the COVID-19 pandemic.