Background  In February 2022, a familial cluster of 2019-nCoV Omicron variant infection occurred in Guangxi Province, China. The clinical characteristics of Omicron infection remain unclear.

  Objective   To investigate the clinical characteristics of local aggregative 2019-nCoV Omicron cases in Guangxi, and provide evidence for its prevention and control.

  Methods  A total of 144 Omicron family cluster infection cases admitted from February 4 to March 2, 2022 in Guangxi were collected. Their serological and biochemical results, vaccination and hospitalization status were statistically analyzed, and the correlation between these clinical features and COVID-19 moderate cases were analyzed by univariate and multivariate Logistic regression.

  Results  Among 144 patients, 80 were male and 64 were female, with an average age of (34.55 ± 18.6) years. Fifty-six cases (38.9%) were classified as mild COVID-19, 86 cases (59.7%) were moderate, and 2 cases (1.4%) were severe, without any critical cases. Moderate cases showed significantly higher lactic dehydrogenase (LDH), alanine aminotransferase (ALT), and aspartate aminotransferase (AST) levels (MdIQR: 185165-219 U/L vs 172152-207 U/L, 2015-31 U/L vs 1611.8-21.2) U/L, 2521-31 U/L vs 2218-30 U/L, all P<0.05), and were older (35 21, 47 years vs 29 18, 37 years, P=0.001) than mild cases. The average length of hospital stay was significantly shorter for patients who had received 3 or 2 doses of vaccine than for those who had received 1 or no dose of vaccine (21.48 ± 5.60 d vs 26.36 ± 5.07 d, 22.22 ± 6.15 d vs 26.36 ± 5.07 d, P<0.05, respectively). During the 1-month follow-up, 6% (8/144) of the patients had occasional mild cough and no other discomfort. Univariate and multivariate Logistic regression analysis showed that age was associated with moderate cases. The risk of moderate cases was 13.519 times higher in older adults than in younger adults (P<0.001).

  Conclusion  In the Omicron family cluster of infections, patients with pulmonary infection (moderate cases) are found to be older and to have stronger biochemical reactions than those with mild cases. Older adults have a higher risk of developing moderate type of COVID-19 than younger adults. Receiving multiple vaccine doses is still an important means of disease prevention and control.