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

Introduction There is limited information describing the course and severity of illness in subjects infected by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) Omicron variant, especially in children. Methods 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. Results Of the 429 subjects (113 [26.3%] children; 239 [55.7%] female; median age, 36 years [IQR 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 (IQR) 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. Discussion 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 SARS-CoV-2 Omicron infection in this study was not as mild as previously suggested. Key Messages What is already known on this topic Previous studies have demonstrated that Omicron patients were more likely to be mild, less hospitalized, less severe disease, and of lower mortality. However, there is limited information describing the course and severity of illness in subjects infected by the Omicron variant, especially in children. What this study adds This study reveals that the prevalence of symptomatic and moderate Covid-19 in Omicron infections was considerably high for children and adults in China. In this population based cohort study of 113 children and 316 adults with Omicron variant infection contracted during the outbreak in Tianjin, China, 95.6% of the subjects were symptomatic on admission. Although children had significantly lower proportions of moderate Covid-19 on admission compared to adults (8.8% vs 44.3%), almost one of ten infected children suffered from moderate COVID-19. How this study might affect research, practice or policy This study expands our understanding of the course and illness severity of the SARS-CoV-2 Omicron infections, especially in children. Awareness and appropriate control policies are needed to reduce moderate illnesses by the Omicron infections.