To the Editor: We read with great interest the article by Park et al. (1) on contact tracing of 5,706 patients with coronavirus disease (COVID-19) during the early phase of the pandemic in South Korea. In the study, the overall detection rate of COVID-19 among household contacts was 11.8%; the highest detection rate (18.6%) was in household contacts of those 10–19 years of age and the lowest detection rate (5.3%) in household contacts of those 0–9 years of age. The media have reported the research as evidence that transmissibility in adolescents and adults is similar (2). Such an interpretation may influence decision-making on the reopening of schools.

Although this study nicely demonstrated the effectiveness of contact tracing strategy during a period of school closure, understanding transmissibility and the implications for the reopening of schools requires reinterpretation of the data. As of April 29, 2020, a total of 37.8% of the 10–19 age group were 19 years of age (223/590) and, therefore, were not school children (3). A recently published study in South Korea (4) reported 107 primary source children (aged 0–18) had 248 household contacts and only 1 became infected, giving a secondary attack rate of 0.5%. Data from source and contact tracing in the Netherlands (5) also confirmed low transmissibility in children <18 years of age (0/43, 0%) compared with persons >18 years (55/566, 8.3%).

Accumulating data, including this study, suggest low transmissibility in infected children <10 years of age. However, transmissibility in the adolescent age group is unclear at this time. The 10–19 years age group includes diverse students who have completely different contact patterns from elementary school through college; thus, transmission dynamics of COVID-19 may be different. Further detailed studies on understanding transmissibility of the virus by each school level can provide helpful insights for safe reopening of schools.

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