U.S. counties with greater social vulnerability were more likely to become areas with rapidly increasing incidence of coronavirus disease 2019 (COVID-19), also known as "hotspots". Among hotspot counties, those with greater social vulnerability had higher COVID-19 incidence during the 14 days after detection: 212 to 234 cases per 100,000 persons for highest social vulnerability index (SVI) quartile, versus 35 to 131 cases per 100,000 persons for other quartiles. Areas defined as hotspot counties met four criteria, relative to the date assessed: Greater than 100 new COVID-19 cases in the most recent seven . . .