SARS-CoV-2 Omicron infection is associated with high nasopharyngeal viral load

Background: We provide here direct comparison of viral load in nasopharyngeal specimens of patients infected by Omicron and former severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) variants. Methods: We retrospectively reviewed the results of SARS-CoV-2 testing conducted during two corresponding periods of years 2021 and 2022 (i.e., between 3-9 January), characterized by local prevalence of Alpha (>95%; January 2021) and Omicron (>90%; January 2022) SARS-CoV-2 variants, respectively. In both years viral load was quantified using the same method and instrumentation (Seegene Allplex SARS-CoV-2 Assay). Results: The total number of patients with positive SARS-CoV-2 tests was 47 in January 2021 and 118 in January 2022, respectively. The cycle threshold (Ct) values in January 2022 (median Ct value, 27.5; IQR, 23.5-32.7) when the Omicron variant was prevalent were significantly lower than those measured during the same period of the year 2021 (median Ct value, 31.8; IQR, 26.4-37.6; p=0.007), when the Alpha variant was prevalent. The rate of subjects with high nasopharyngeal viral load was over 2-fold higher in January 2022 than in January 2021 (45/118 vs. 10/47; Odds ratio, 2.28 and 95%CI, 1.03-5.03; p=0.041). Conclusions: These results support the suggestion that aerosols released by patients infected by SARS-CoV-2 Omicron variant may contain higher viral particles than those released by subjects infected with previous strains.