Since the start of the COVID-19 pandemic, thousands of scientists and volunteers have been tracking the interventions that governments have adopted to curb viral spread - from closing restaurants to mandating face masks. They hope to deduce which policies are most effective. At a conference this month, scientists involved in 50 tracking databases discussed their efforts. Peter Klimek, a mathematical physicist at the Complexity Science Hub (CSH) Vienna and the Medical University of Vienna, who is involved in the CSH's tracking project, explains the challenge.