Objective:To analyze the clinical characteristics of patients infected with 2019-nCoV Omicron variants BA.1 and BA.2 in Zhuhai city.Methods:A retrospective study was conducted to compare clinical characteristics of patients infected with 2019-nCoV Omicron variants BA.1 and BA.2, who were admitted in the Fifth Affiliated Hospital of Sun Yat-sen University during January 13 to March 8 2022. The Mann-Whitney U-test or Kruskal-Wallis H test was used for quantitative data, and the χ2 test or Fisher’s exact test was used for qualitative data. Results:Among 122 patients infected with the Omicron variant, there was 79 adults (BA.1 23 cases, BA.2 56 cases) and 43 children (BA.1 19 cases, BA.2 24 cases). In adults, patients infected with BA.2 sub-variant had a higher baseline viral loads at admission than BA.1 infected patients [7.64(6.92, 8.55) lg copies/mL vs. 6.64(6.04, 7.34) lg copies/mL; Z=-3.022, P=0.003]; compared to BA.1 patients, BA.2 patients had a higher proportion of mild and asymptomatic cases and a lower proportion of common infection cases ( χ2=8.052, P=0.012); the proportion of patients with pneumonia imaging changes in BA.1 patients was higher than that in BA.2 infected patients [(6/23, 26.1%) vs. (2/56, 3.6%); χ2=6.776, P=0.009). In children, the rate of fever in BA.2 group was higher than that in BA.1 group [(16/24, 66.7%) vs. ( 5/19, 26.3%); χ2=6.910, P=0.009); the proportion of patients with reduced lymphocyte counts in BA.2 group was higher than that in BA.1 group [(17/24, 70.8%) vs.(1/19, 5.3%); χ2=18.734, P<0.001). Compared with adult cases, children with BA.2 sub-variant infection had higher fever rate [(16/24, 66.7%) vs. (19/56, 33.9%); χ2=7.317, P=0.007). The viral loads of daily nasal swabs in BA.2 infected patients increased first and then decreased in both adults and children, with a greater decrease than BA.1 during the first two weeks. Conclusions:Compare with 2019-nCoV Omicron variant BA.1, BA.2 has a higher baseline viral loads in adults, which means much more contagious in the early stages. But the viral load drops faster in BA.2 infected patients. In children, BA.2 patients are more likely to have fever and reduced lymphocyte counts, which indicates that the prevention and control of 2019-nCoV Omicron sub-variant BA.2 is more difficult.