Comparative evaluation of swabbing sites for Omicron variant detection in PCR testing

The Omicron variant of SARS-CoV-2 raised concerns about the best sampling sites for PCR testing, with early indications suggesting throat swab samples were better than nasal swab samples. Our study evaluated the sensitivity of detecting SARS-CoV-2 across different swabbing sites. Participants undergoing testing at NHS Test and Trace sites in England provided self-collected samples using nose only, throat only, and combined nose and throat swabs, which were analysed by realtime PCR. Among 815 participants, combined swabs had higher viral concentrations than nose only or throat only swabs. Sensitivity for detecting SARS-CoV-2 by PCR was 91 % for nose only and 97 % for throat only, relative to the combined approach. VC remained stable in nose swabs but declined in throat swabs with time. Combined nose and throat swabbing remains the most effective method for SARS-CoV-2 detection. If a single swab is used, a throat swab has a higher sensitivity than nose swabs, although VC in the throat decreases faster in later infection stages. The variations in VC over time and intra-person variation between sampling sites underscore the complexity of viral dynamics, highlighting the importance of considering both nose and throat samples for comprehensive testing.