Coordinated lockdown strategies among countries is key to preventing resurgent COVID-19 outbreaks in continental Europe, a new modeling study shows. A continental epidemic could occur as many as five weeks earlier when well-connected countries with stringent existing interventions end their interventions prematurely, the study's authors say. As rates of new COVID-19 cases begin to decline in countries around the world, governments are considering how to ease restrictions without disease resurgence. This includes lifting non-pharmaceutical interventions such as social distancing policies and lockdown measures in a coordinated way that prevents international travel from causing resurgent epidemics. While such efforts are generally considered important, evidence informing how countries should implement them, and of their potential benefits, is lacking. To better quantify the value of coordinated exit strategies, Nick Ruktanonchai and colleagues took advantage of the way data from mobile phones can inform contact rates between people and the effect of interventions on human mobility. With data provided Vodafone and Google, they modelled the spread of COVID-19 under different coordinated and uncoordinated exit strategy scenarios using an openly available epidemiological model of COVID-19 transmission. Across 1200 simulations, they found that synchronized cycles of interventions were always more likely to end community transmission. In the most striking example, synchronizing four cycles of three-week long lockdowns led to local elimination of COVID-19 cases in 90% of simulations, while unsynchronized cycles only led to elimination 5% of the time. Importantly, say the authors, their simulations do not include any importation from other regions of the globe. "The implications of our study extend well beyond Europe and COVID-19," say Ruktanonchai and colleagues, "broadly demonstrating the importance of communities coordinating easing of various non-pharmaceutical interventions for any potential pandemic."