Viral load of SARS‐CoV‐2 Omicron is not high despite its high infectivity
Sonoka Yuasa, Jun Nakajima, Yuna Takatsuki, Yuta Takahashi, Chihiro Tani‐Sassa, Yumi Iwasaki, Katsutoshi Nagano, Kazunari Sonobe, Tomoyo Yoshimoto, Yoko Nukui, Hiroaki Takeuchi, Kousuke Tanimoto, Yukië Tanaka, Akinori Kimura, Naoya Ichimura, Shuji Tohda
Abstract
Abstract Patients infected with the Omicron variant of severe acute respiratory syndrome coronavirus 2 has increased worldwide since the beginning of 2022 and the variant has spread more rapidly than the Delta variant, which spread in the summer of 2021. It is important to clarify the cause of the strong transmissibility of the Omicron variant to control its spread. In 694 patients with coronavirus disease 2019, the copy numbers of virus in nasopharyngeal swab‐soaked samples and the viral genotypes were examined using quantitative polymerase chain reaction (PCR) and PCR‐based melting curve analysis, respectively. Whole‐genome sequencing was also performed to verify the viral genotyping data. There was no significant difference ( p = 0.052) in the copy numbers between the Delta variant cases (median 1.5 × 10 5 copies/μl, n = 174) and Omicron variant cases (median 1.2 × 10 5 copies/μl, n = 328). During this study, Omicron BA.1 cases (median 1.1 ×10 5 copies/μl, n = 275) began to be replaced by BA.2 cases (median 2.3 × 10 5 copies/μl, n = 53), and there was no significant difference between the two groups ( p = 0.33). Our results suggest that increased infectivity of the Omicron variant and its derivative BA.2 is not caused by higher viral loads but by other factors, such as increased affinity to cell receptors or immune escape.