To analyze this cryptic transmission phase and the first wave of the pandemic that ensued, researchers from Italy, UK, and the US used a data-driven, spatial, stochastic, and age-structured epidemic model. They developed a mechanistic understanding of the evolution of the epidemic and estimated the time required for local transmission in various states and countries. The model developed by the team offers a statistical idea of SARS-CoV-2 introductions across European countries and many states in the US.