Detection of Higher Cycle Threshold Values in Culturable SARS-CoV-2 Omicron BA.1 Sublineage Compared with Pre-Omicron Variant Specimens — San Francisco Bay Area, California, July 2021—March 2022
Michel Tassetto, Miguel Garcia-Knight, Khamal Anglin, Scott Lu, Amethyst Zhang, Mariela Romero, Jesus Pineda-Ramirez, Ruth Diaz Sanchez, Kevin C. Donohue, Karen Pfister, Curtis Chan, Sharon Saydah, Melissa Briggs‐Hagen, Michael J. Peluso, Jeffrey N. Martin, Raul Andino, Claire M. Midgley, J. Daniel Kelly
Abstract
(6,7) of nonhospitalized participants with positive SARS-CoV-2 test results living in the San Francisco Bay Area** were used to generate Ct values and assess for the presence of culturable SARS-CoV-2 virus; findings were compared between specimens from participants infected with pre-Omicron variants and those infected with the Omicron BA.1 sublineage. Among specimens with culturable virus detected, Ct values were higher (suggesting lower RNA levels) during Omicron BA.1 infections than during pre-Omicron infections, suggesting variant-specific differences in viral dynamics. Supporting CDC guidance, these data show that Ct values likely do not provide a consistent proxy for infectiousness across SARS-CoV-2 variants.