Characterization of Severe Acute Respiratory Syndrome Coronavirus 2 Omicron Variant Shedding and Predictors of Viral Culture Positivity on Vaccinated Healthcare Workers With Mild Coronavirus Disease 2019

Abstract

In this prospective cohort of 30 vaccinated healthcare workers with mild Omicron variant infection, we evaluated viral culture, rapid antigen test (RAT), and real-time reverse-transcription polymerase chain reaction (RT-PCR) of respiratory samples at days 5, 7, 10, and 14. Viral culture was positive in 46% (11/24) and 20% (6/30) of samples at days 5 and 7, respectively. RAT and RT-PCR (Ct ≤35) showed 100% negative predictive value (NPV), with positive predictive values (PPVs) of 32% and 17%, respectively, for predicting viral culture positivity. A lower RT-PCR threshold (Ct ≤24) improved culture prediction (PPV = 39%; NPV = 100%). Vaccinated persons with mild Omicron infection are potentially transmissible up to day 7. RAT and RT-PCR might be useful tools for shortening the isolation period.

Keywords: Omicron variant; RT-PCR; SARS-CoV-2; rapid antigen test; viral culture.

Figure 1.

Comparison of SARS-CoV-2 RT-PCR Ct values by having received a booster dose (“Booster dose”) of any COVID-19 vaccine, primary vaccination with CoronaVac (“CoronaVac”) or other vaccines, previous infection with SARS-CoV-2 (“Previous infection”), and viral culture positivity (Culture positive) on each day of symptoms.

Figure 2.

Real-time reverse-transcription polymerase chain reaction, rapid antigen test, and viral culture positivity (with 95% confidence interval) by days since symptom onset in persons infected with severe acute respiratory syndrome coronavirus 2 Omicron variant. Abbreviations: Ct, cycle threshold; RAT, rapid antigen test; RT-PCR, real-time reverse-transcription polymerase chain reaction.