Background: Population-level initiatives to address the mental health issues arising from the COVID-19 pandemic have been described in the literature but have not always been collated in a way that can directly inform policy and practice decision-making. Furthermore, identifying which population-level interventions are most effective at targeting which mental health concerns, at population-level, in a post-covid world remains a policy and practice challenge. Aims and Methods: To support greater engagement with current policy-demands to address a population-mental health crises we drew on global prevalence data reported in systematic reviews. Systematic reviews were sourced from a Living Map of COVID-19, described and critically appraised. Findings were presented to key stakeholders to inform a systematic review of population-level mental health interventions. Results and discussion: Identifying reliable estimates of any increase in mental health issues as a result of COVID-19 remains a challenge. Despite best efforts, systematic reviews were hampered by a number of methodological limitations. Although meta-analysis of longitudinal data was available for adult populations, data on children and young people was dominated by narrative synthesis methods. Conclusion: Methods for drawing on review-level evidence of prevalence data to inform systematic reviews of interventions is still relatively new. Doing so, can increase policy and practice relevance when methodological issues are understood and addressed.