The purpose of the present study was to propose and test two models to understand the relationship between perceived vulnerability to COVID-19 (PVC) and COVID-19-related traumatic stress (TS), as well as the variables that may mediate and moderate this relationship among individuals who have not yet been infected with COVID-19 . Using an online survey, data were collected between late March and early April 2020 . Participants were recruited through Amazon Mechanical Turk and included 747 adults living in the United States . Supporting our hypotheses, results indicated that both COVID-19-related worries and social isolation were significant mediators of the relationship between PVC and TS (Model 1). In addition, the results of a moderated mediation analysis indicated that the indirect effect of PVC on TS through COVID-19-related worries was stronger for participants who reported greater social isolation (Model 2). Although future research is needed, these findings suggest that both social isolation and disease-related worries may be important variables that can be targeted in interventions to reduce pandemic-related TS.