A Unique Clade of SARS-CoV-2 Viruses is Associated with Lower Viral Loads in Patient Upper Airways.

The rapid spread of SARS-CoV-2, the causative agent of Coronavirus disease 2019 (COVID-19), has been accompanied by the emergence of distinct viral clades, though their clinical significance remains unclear. Here, we examined the genome sequences of 88 SARS-CoV-2 viruses from COVID-19 patients in Chicago, USA and identified three distinct phylogenetic clades. Clade 1 was most closely related to clades centered in New York, and showed evidence of rapid expansion across the USA, while Clade 3 was most closely related to those in Washington. Clade 2 was localized primarily to the Chicago area with limited evidence of expansion elsewhere. Average viral loads in the airways of patients infected with the rapidly spreading Clade 1 viruses were significantly higher than those of the poorly spreading Clade 2. These results show that multiple variants of SARS-CoV-2 are circulating in the USA that differ in their relative airway viral loads and potential for expansion.