In February 2016, the World Health Organization declared the Zika epidemic an international public health emergency. Before long, the virus became rampant in the Americas, but its precise date of entry and dynamics of spread remain unclear. Using a high-resolution epidemic model that incorporates physical, demographic, and mosquito-related factors, Qian Zhang et al. found that the virus may have first arrived in Brazil between August 2013 and April 2014, thus ruling out the June 2014 soccer World Cup, a previously suspected moment of entry. Further, Haiti, Honduras, and Puerto Rico had a higher number of new infections relative to population sizes, compared with Mexico and Colombia. Notably, the model predicted the number of newborn children from infected women through December 2017 in several affected countries, thus providing potential estimates of the number of pregnancies at risk of developing microcephaly and other birth defects. The model also estimated that approximately 57,910 new Zika infections were imported into the continental United States by early October 2016, a figure comparable to the roughly 83,700 new infections estimated using data from the Centers from Disease Control and Prevention. According to the authors, the findings might help researchers select sites for future Zika vaccine trials.