[Characteristics of SARS-CoV-2 Omicron infection in children imported from Hong Kong].

Objective: To understand the clinical characteristics of children with SARS-CoV-2 Omicron infection imported from Hong Kong Special Administrative Region. Methods: This retrospective study was conducted to collect the data including clinical manifestations, outcomes and vaccination of 107 children with SARS-CoV-2 Omicron infection imported from Hong Kong Special Administrative Region to be admitted to the designated referral hospital in Shanghai from February to March 2022. According to the occurrence of clinical symptoms, the cases were divided into asymptomatic group and symptomatic group. According to the age of diagnosis, the cases were divided into <3 years group, 3-<6 years group and 6-<18 years group, and the clinical manifestations in different age group were analyzed with t-test and Mann-Whitney rank-sum test. Besides, to analyze the effectiveness of vaccination against SARS-CoV-2 Omicron infection in different age group, the cases aged 3-<18 years were also subdivided into unvaccinated group, 1-dose group and 2-dose group, and the relative risk (RR) was used to demonstrate the effectiveness. Results: Among the 107 cases, 66 were male and 41 were female, with infection age of 10 (5, 14) years. There were 29 cases in the asymptomatic group, and 78 cases in the symptomatic group, and no significant difference in the age of infection was observed between the 2 groups (11 (6, 14) vs. 10 (5, 14) years, Z=0.49, P>0.05). And there were no severe cases in symptomatic group. The length of hospitalization was (18±6) days, and was longer in symptomatic group than that in asymptomatic group ((19±6) vs. (16±7) d, t=0.17, P=0.030). Eight-two cases (76.6%) had a history of epidemiological exposure and, among whom, 81 cases (75.7%) were associated with household transmission. Among symptomatic group, 57 cases (73.1%) had fever and 20 cases (25.6%) had cough. Of the 74 cases undergoing chest CT examination, 17 cases (23.0%) showed mild abnormalities. Of the 83 cases who received the lab tests, 23 cases (27.7%) had white blood cell counts<4×109/L, 3 cases (3.6%) had C-reaction protein >8.0 mg/L, and 6 cases (7.2%) had slightly elevated aspartate transaminase and alanine aminotransferase. Among the 92 children aged 3-<18 years, 31 cases were unvaccinated, 34 cases received 1 dose, and 27 cases received 2 doses. The interval between the last vaccination and infection was 2.2 (0.6, 6.0) months; the interval between the last vaccination and infection in the 2-dose group was longer than that in 1-dose group (6.0 (4.5, 7.3) vs. 0.7 (0.3,2.0) months, Z=3.59, P<0.001).The risk of symptomatic infection was reduced by 45% (RR=0.55, 95% CI 0.35-0.87) with two-dose vaccination compared to non-vaccination in cases aged 3-<18 years. All these cases recovered completely. Conclusions: Children infected with SARS-CoV-2 Omicron are usually mild or asymptomatic. Household transmission is the main pattern of infection with SARS-CoV-2 Omicron in children. Two-dose SARS-CoV-2 vaccination in children aged 3-<18 years can provide partial protection against disease caused by SARS-CoV-2 Omicron.目的： 了解香港特别行政区输入性新型冠状病毒Omicron株感染患儿的临床特征。 方法： 回顾性研究，收集2022年2至3月上海市新型冠状病毒感染患儿定点转诊医院收治的107例香港特别行政区输入性新型冠状病毒感染患儿的临床表现及转归、疫苗接种状况等资料。根据是否出现临床症状分为无症状感染组和症状感染组，按照感染年龄将患儿分为<3岁、3~<6岁和6~<18岁组，根据疫苗接种状态将3~<18岁患儿分为未接种组、接种1剂次组、接种2剂次组。组间比较采用t检验和Mann-Whitney秩和检验，采用相对危险度（RR）评估不同年龄患儿接种疫苗对儿童感染新型冠状病毒的保护作用。 结果： 107例新型冠状病毒感染患儿中男66例、女41例，感染年龄10（5，14）岁。无症状感染组29例、症状感染组78例，2组间感染年龄差异无统计学意义［11（6，14）比10（5，14）岁，Z=0.49，P>0.05］；症状感染组中无重型患儿。107例患儿住院时间为（18±6）d，症状感染组住院时间长于无症状感染组［（19±6）比（16±7）d，t=0.17，P=0.030］。82例（76.6%）患儿有明确的确诊病例接触史，其中81例（75.7%）与家庭内传播关联。症状感染组患儿中常见症状为发热57例（73.1%），咳嗽20例（25.6%）。74例患儿接受胸部CT检查，17例（23.0%）表现轻度异常。83例患儿接受外周血检查，23例（27.7%）白细胞计数<4×109/L，3例（3.6%）C反应蛋白>8.0 mg/L，6例（7.2%）天冬氨酸转氨酶和丙氨酸转氨酶轻度升高。92例3~<18岁患儿中，未接种组31例、接种1剂次组34例、接种2剂次组27例。末次接种与确诊感染的时间间隔为2.2（0.6，6.0）个月。末次接种与确诊感染的时间间隔在接种2剂次疫苗组中长于接种1剂次疫苗组［6.0（4.5，7.3）比0.7（0.3，2.0）个月，Z=3.59，P<0.001）］。症状感染组3~<18岁接种2剂次疫苗较未接种疫苗患儿的感染风险降低45%（RR=0.55，95%CI 0.35~0.87）。107例患儿均治愈出院。 结论： 儿童新型冠状病毒Omicron株感染通常轻型或无症状。家庭内传播是儿童感染新型冠状病毒 Omicron株的主要模式。3~<18岁儿童接种2剂次新型冠状病毒灭活疫苗对新型冠状病毒Omicron株感染引起的疾病提供部分保护作用。.