The COVID-19 pandemic had a global impact on mental health. Identification of individuals at higher or lower risk of mental health problems may assist with targeting prevention, support and treatment efforts during future pandemics. Using a Canadian national mental health survey that collected data during the pandemic period (March 2022–December 2022), this study examined the vulnerability of participants reporting abuse during their childhood by examining the annual prevalence of mood, anxiety and substance use disorders. Psychiatric disorders were identified using a version of the Composite International Diagnostic Interview (CIDI). Because childhood adversities are well-known risk factors for mental disorders, the analysis focused on interactions between childhood adversities and pandemic-related stressors by estimating the relative excess risk due to interaction (RERI). RERIs provide evidence of synergy based on the occurrence of greater than additive interactions. Physical and sexual abuse interacted synergistically with pandemic-related stressors in predicting mood and anxiety disorders. No synergies were found for substance use disorders. Childhood adversities increase vulnerability to later stressors and may be useful for the identification of individuals more likely to have mental health needs during this type of public health emergency.