Course and clinical severity of the SARS-CoV-2 Omicron variant infection in Tianjin, China

There is limited information describing the course and severity of illness in subjects infected by the severe acute respiratory syndrome coronavirus 2 Omicron variant, especially in children. In this population-based cohort study, subjects with Omicron variant infection during the outbreak between January 8 and February 12, 2022 in Tianjin, China were included (n = 429). The main outcomes were the distribution of asymptomatic, mild, moderate, and severe patients, and clinical courses including the interval from positive polymerase chain reaction (PCR) test to the onset, aggravation or relief of symptoms, and the interval of reversing positive PCR-test into negative, and length of hospital stay. Of the 429 subjects (113 [26.3%] children; 239 [55.7%] female; median age, 36 years [interquartile range 15.0 to 55.0 years]), the proportion (95% CI) of symptomatic subjects on admission was 95.6% (93.2%, 97.2%), including 60.4% (55.7%, 64.9%) mild, 35.0% (30.6%, 39.6%) moderate, and 0.2% (0.0%, 1.3%) severe. Compared with adults, children had lower proportion of moderate Covid-19 (8.8% vs 44.3%). On discharge, 45.9% (41.3%, 50.7%) and 42.2% (37.6%, 46.9%) of the subjects were diagnosed as having experienced mild and moderate Covid-19. The median (interquartile range) length of hospital stay was 14.0 (12.0, 15.0) days. The median interval of reversing positive PCR-test into negative was 12.0 (10.0, 13.0) days. Symptomatic and moderate Covid-19 in Omicron infections was common in adults and children, recovery from Omicron infections took around 2 weeks of time. The severe acute respiratory syndrome coronavirus 2 Omicron infection in this study was not as mild as previously suggested.