Daily COVID-19 Stressor Effects on Children's Mental Health Depend on Pre-pandemic Peer Victimization and Resting Respiratory Sinus Arrhythmia.

Children's risk of poorer mental health due to the COVID-19 pandemic may depend on risk and protective factors heading into the pandemic. This study examined same-day associations between COVID-19 stressors and children's mental health using a daily diary design across 14 days, and considered the moderating roles of pre-pandemic peer victimization experiences and resting respiratory sinus arrhythmia (RSA; an indicator of cardiac regulatory capacity). Forty-nine Canadian children aged 8-13 years (M age  = 10.69, 29 girls) participated in the final wave of a longitudinal study just prior to the pandemic and a daily diary extension during the pandemic (N = 686 pandemic measurement occasions). Multilevel modeling indicated that children had poorer mental health on days when they experienced a COVID-19 stressor (e.g., virtual academic difficulties, social isolation). A three-way interaction indicated that this association was stronger for those with higher pre-pandemic peer victimization experiences and lower pre-pandemic resting RSA; however, highly victimized children with higher resting RSA did not experience poorer mental health on days with COVID-19 stressors. Findings offer preliminary insights into the preceding risk and protective factors for children's mental health amidst major subsequent stress.