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

Abstract

In the COVID-19 outbreak, caused by SARS-CoV-2, more than 111 million people have been infected and more than 2.4 million individuals have died worldwide.¹ The first COVID-19 patient in Hong Kong was diagnosed on January 23, 2020.² Hong Kong is now experiencing its fourth wave of COVID-19 outbreaks, during which multiple public health policies have been implemented to facilitate social distancing to reduce the spread of COVID-19.³ These public health policies have had a far greater impact than expected, and nearly all children and youths with COVID-19 in Hong Kong have had only mild illness.^4,5 During the 4 COVID-19 outbreaks, the Government of Hong Kong implemented territory-wide school closures intermittently.^6,7 During each school closure, face-to-face teaching was replaced by homeschooling and online classes. Students attended classroom lessons for less than 3 months in 2020. A 2020 large-scale local study⁸ found that the prolonged school closures may have been associated with increased risk among children of developing psychosocial problems, which were associated with decreased emotional and social functioning and decreased physical activity levels. Existing inequalities, such as having children with special educational needs, in families with increased risk of psychosocial problems were associated with increased levels of these adverse outcomes. A 2020 study⁹ in the US found that SARS-CoV-2 infection in children and youths was not associated with attending school or childcare centers, and a 2021 study¹⁰ in the US found that secondary transmission of SARS-CoV-2 within schools was rare. However, evidence concerning the COVID-19 outbreaks in schools in Hong Kong is lacking. Furthermore, To et al¹¹ found that the predominant circulating strains of SARS-CoV-2 in Hong Kong were different in each of the 3 waves, which could possibly influence the clinical characteristics of children and youths infected in the 3 waves. Therefore, we conducted this study to compare the clinical characteristics and identify the sources of infection among children and youths with COVID-19 during the first 3 waves of outbreaks in Hong Kong.