Two opposing forces that are shaping the coronavirus disease 2019 (Covid-19) pandemic are the emergence of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) variants of concern and the uptake of vaccines. Measurement of SARS-CoV-2 viral load over the course of acute infection can inform hypotheses about the mechanisms that underlie variation in transmissibility according to variant and vaccination status. Recent evidence suggests that infections with the delta variant feature higher peak viral loads than those in other lineages and that vaccine recipients who are infected with SARS-CoV-2 may clear the infection more quickly than unvaccinated persons. However, descriptions of SARS-CoV-2 viral dynamics have been principally based on cross-sectional studies in which testing was triggered by the onset of symptoms. Such study designs overlook viral dynamics during the early stages of infection and introduce bias in viral load measurements from different periods of the pandemic. To overcome these limitations, we collected and analyzed a prospective, longitudinal set of 19,941 SARS-CoV-2 viral samples obtained from 173 participants as part of the occupational health program of the National Basketball Association between November 28, 2020, and August 11, 2021.

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