Quantifying the spatiotemporal dynamics of the first two epidemic waves of SARS-CoV-2 infections in the United States

SARS-CoV-2 infection rates displayed striking temporal and spatial variation during the emergence of new variants globally and within the United States. While spatiotemporal "waves" of infection have been observed, quantitative assessments of their spread remain limited. Here, we estimate and compare the speed and spatial extent of the first two major infection waves in the United States, illustrating these dynamics through detailed visualizations. Our findings reveal that the origins of these waves coincide with large gatherings and the relaxation of masking mandates. Notably, the second wave spread more rapidly than the first, driven by multiple, non-contiguous origins of infection. This highlights the role of regional heterogeneity in epidemic dynamics and underscores the importance of localized public health measures in mitigating ongoing outbreaks.