Finding psychological factors that can reduce the substantial impact of COVID-19 on mental and physical health is important. Here we replicate and expand a previous study regarding the role of psychological flexibility (PF) in this context. We employed a comprehensive and well validated measure of PF and examined its role in relation to health outcomes and persistent post COVID-19 symptoms. 1174 participants completed standardized measures of depression, anxiety, insomnia and the Multidimensional Psychological Flexibility Inventory (MPFI), and reported the presence of persistent symptoms associated with "long COVID." All PF and psychological inflexibility (PI) facets, except for acceptance, correlated with the three mental health outcomes and with persistent symptoms. PF and PI accounted for significant variance in depression, anxiety, and insomnia after adjusting for background and health status variables. A notable finding was the particularly stronger correlations obtained for the PI facets. Our findings emphasize the potentially mitigating effects of PF on mental ill health, as well as the particularly aggravating effects of PI, in the pandemic context. A novel finding is the significant association of PI with persisting symptoms of COVID.