Clinical Characteristics and Transmission of COVID-19 in Children and Youths During 3 Waves of Outbreaks in Hong Kong

Abstract

Importance: Schools were closed intermittently across Hong Kong to control the COVID-19 outbreak, which led to significant physical and psychosocial problems among children and youths.

Objective: To compare the clinical characteristics and sources of infection among children and youths with COVID-19 during the 3 waves of outbreaks in Hong Kong in 2020.

Design, setting, and participants: This cross-sectional study involved children and youths aged 18 years or younger with COVID-19 in the 3 waves of outbreaks from January 23 through December 2, 2020. Data were analyzed from December 2020 through January 2021.

Main outcomes and measures: Demographic characteristics, travel and contact histories, lengths of hospital stay, and symptoms were captured through the central electronic database. Individuals who were infected without recent international travel were defined as having domestic infections.

Results: Among 397 children and youths confirmed with COVID-19 infections, the mean (SD) age was 9.95 (5.34) years, 220 individuals (55.4%) were male, and 154 individuals (38.8%) were asymptomatic. There were significantly more individuals who were infected without symptoms in the second wave (59 of 118 individuals [50.0%]) and third wave (94 of 265 individuals [35.5%]) than in the first wave (1 of 14 individuals [7.1%]) (P = .001). Significantly fewer individuals who were infected in the second and third waves, compared with the first wave, had fever (first wave: 10 individuals [71.4%]; second wave: 22 individuals [18.5%]; third wave: 98 individuals [37.0%]; P < .001) or cough (first wave: 6 individuals [42.9%]; second wave: 15 individuals [12.7%]; third wave: 52 individuals [19.6%]; P = .02). Among all individuals, 394 individuals (99.2%) had mild illness. One patient developed chilblains (ie, COVID toes), 1 patient developed multisystem inflammatory syndrome in children, and 1 patient developed post-COVID-19 autoimmune hemolytic anemia. In all 3 waves, 204 patients with COVID-19 (51.4%) had domestic infections. Among these individuals, 186 (91.2%) reported having a contact history with another individual with COVID-19, of which most (183 individuals [90.0%]) were family members. In the third wave, 18 individuals with domestic infections had unknown contact histories. Three schoolmates were confirmed with COVID-19 on the same day and were reported to be close contacts.

Conclusions and relevance: This cross-sectional study found that nearly all children and youths with COVID-19 in Hong Kong had mild illness. These findings suggest that household transmission was the main source of infection for children and youths with domestic infections and that the risk of being infected at school was small.

Figure.. Admissions of Children and Youths With COVID-19 in Hong Kong

Kindergarten year 1 and 2 students were not allowed to return to school from January 24 through September 29, 2020. Secondary year 3 to 5 students resumed classes on May 27, 2020; primary year 4 to 6 and secondary year 1 and 2 students resumed classes on June 8, 2020; kindergarten year 3 and primary year 1 to 3 students resumed classes on June 15, 2020. Summer holiday began on July 14, 2020, and extended through September 23, 2020. Kindergarten year 3; primary year 1, 5, and 6; and secondary year 1, 5, and 6 students resumed classes on September 23, 2020; kindergarten year 1 and 2, primary year 2 to 4, and secondary year 2 to 4 students resumed classes on September 29, 2020. Kindergarten year 1 to 3 and primary year 1 to 3 classes were closed on November 14 and November 23, 2020, respectively, owing to outbreaks of non-COVID-19–related upper respiratory tract infections; primary year 4 to 6 and all secondary school classes were closed on December 2, 2020, owing to the wave 4 COVID-19 outbreak. HKDSE indicates Hong Kong Diploma of Secondary Education examination period.