Viral Dynamics of Omicron and Delta Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) Variants With Implications for Timing of Release from Isolation: A Longitudinal Cohort Study.

Background: In January 2022, US guidelines shifted to recommend isolation for 5 days from symptom onset, followed by 5 days of mask-wearing. However, viral dynamics and variant and vaccination impact on culture conversion are largely unknown.
Methods: We conducted a longitudinal study on a university campus, collecting daily anterior nasal swabs for at least 10 days for reverse-transcription polymerase chain reaction (RT-PCR) testing and culture, with antigen rapid diagnostic testing (RDT) on a subset. We compared culture positivity beyond day 5, time to culture conversion, and cycle threshold trend when calculated from diagnostic test, from symptom onset, by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) variant, and by vaccination status. We evaluated sensitivity and specificity of RDT on days 4-6 compared with culture.
Results: Among 92 SARS-CoV-2 RT-PCR-positive participants, all completed the initial vaccine series; 17 (18.5%) were infected with Delta and 75 (81.5%) with Omicron. Seventeen percent of participants had positive cultures beyond day 5 from symptom onset, with the latest on day 12. There was no difference in time to culture conversion by variant or vaccination status. For 14 substudy participants, sensitivity and specificity of day 4-6 RDT were 100% and 86%, respectively.
Conclusions: The majority of our Delta- and Omicron-infected cohort culture-converted by day 6, with no further impact of booster vaccination on sterilization or cycle threshold decay. We found that rapid antigen testing may provide reassurance of lack of infectiousness, though guidance to mask for days 6-10 is supported by our finding that 17% of participants remained culture-positive after isolation.
Competing Interests: Potential conflicts of interest. D. H. H. reports funding from the Centers for Disease Control and Prevention for GeoSentinel (1 U01CK000632-01-00) paid to institution and unrelated to this study; personal consulting fees from Major League Soccer, Equinox, Xenophon Strategies, PGA of America; legal consulting fees from Hamilton, Miller & Birthisel, LLP; an unpaid role as data and safety monitoring board chair for a randomized trial to determine the effect of vitamin D and zinc supplementation for improving treatment outcomes among coronavirus disease 2019 patients in India (COVEDZ); and an unpaid volunteer position as secretary–treasurer for the GeoSentinel Foundation, Inc. C. M. K. reports grants or contracts unrelated to this work from NIH NIGMS, Uniformed Services University, BU, and DARPA; consulting fees paid to author from Adventus Research + Consulting, Inc; a leadership or fiduciary role on the Biomedical Engineering Society Board (member) and the American Institute for Medical and Biological Engineering; and 3.0% ownership and cofounder of BioSens8, LLC. J. H. C. reports funding (supports SARS-CoV-2 variant) from Mass CPR/Evergrande and consulting fees paid to author from Cell Signaling Technologies. T. C. B. reports grants or contracts unrelated to this work from Gilead Sciences, Inc and Fujifilm Pharmaceuticals U.S.A., Inc. Z. Z. reports grants or contracts unrelated to this work. All remaining authors: No reported conflicts of interest. All authors have submitted the ICMJE Form for Disclosure of Potential Conflicts of Interest. Conflicts that the editors consider relevant to the content of the manuscript have been disclosed.
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