By Richard R. Watkins, MD, MS, FACP, FIDSA, FISAC

Professor of Internal Medicine, Northeast Ohio Medical University, Rootstown, OH

SYNOPSIS: A surveillance study from Singapore found a very low risk of COVID-19 transmission for children in schools, especially preschools.

SOURCE: Yung CF, Kam K, Nadua KD, et al. Novel coronavirus 2019 transmission risk in educational settings. Clin Infect Dis 2021;72:1055-1058.

Although children generally have less severe illness due to novel coronavirus disease 2019 (COVID-19) compared to other age groups, cases of severe illness and the development of multisystem inflammatory syndrome in children (MIS-C) are concerning to healthcare providers and parents alike. The risks associated with transmission of COVID-19 in children have not been fully elucidated. Therefore, Yung and colleagues aimed to identify these risks in schools to better inform public health control policies.

The study was conducted using a comprehensive nationwide surveillance program in Singapore. In February and March 2020, three potential COVID-19 seeding incidences occurred in three separate educational settings: two preschools and one secondary school. Students with a close contact were placed into quarantine for 14 days from the exposure. Those in quarantine who developed fever or respiratory symptoms were admitted to the hospital and needed at least two negative nasopharyngeal (NP) swabs taken on two separate days to be discharged. Schools were not routinely closed when a positive case was detected, but other containment measures were implemented, such as canceling extracurricular activities, performing terminal cleaning, and staggering recess breaks. However, one of the preschools was closed for 14 days after several staff members tested positive.

In the first incidence, a 12-year-old student attending a secondary school became infected by a family member. The student attended school on the first day of symptoms, then was diagnosed with COVID-19 and hospitalized. Eight students (mean age 12.8 years) who were close contacts (i.e., in the same classroom) developed symptoms, and all subsequently tested negative for COVID-19. In the second incidence, a 5-year-old also became infected by a family member and attended preschool on the first day of symptoms. Thirty-four preschool students (mean age 4.9 years) developed symptoms during the incubation period and were tested for COVID-19, all of whom were negative. The third incidence involved a cluster of 16 adult staff members at a preschool. Seventy-seven children (73% of the total enrollees, mean age 4.1 years) were evaluated, of whom eight were symptomatic and 69 were asymptomatic. All tested negative for COVID-19. The remaining 27% who were not tested did not develop any symptoms while under close monitoring and quarantine.

In all three instances, approximately 40% of symptomatic individuals were tested by multiplex polymerase chain reaction (PCR) for other viral pathogens. Approximately half were positive for rhinovirus, adenovirus, or metapneumovirus.


The major finding of the study by Yung et al was that no documented cases of COVID-19 transmission occurred in children from two preschools and one secondary school following exposure to symptomatic individuals. This suggests that the risk of transmission for children in these settings is low. Indeed, children appear to be at less risk for COVID-19 than for other viral illnesses, such as influenza. Although the underlying mechanism for the reduced risk of COVID-19 infection in children seen in this and other studies remains uncertain, one possible explanation is that young children express fewer ACE2 genes. The spike protein of SARS-CoV-2 binds to the ACE2 receptor on respiratory epithelial cells prior to entry.1 Thus, children might be less susceptible to SARS-CoV-2 on a cellular level. However, recent reports have shown an increase in affinity for ACE2 receptors by SARS-CoV-2 variants, including the B.1.1.7 and B.1.351 strains.2 How this will affect the risk of infection by novel coronavirus variants in children remains to be determined.

The study had some limitations. First, the interval between the timing of sample collection and the last exposure ranged from five to 11 days. However, the authors noted it was unlikely that the timing of sample collection would have missed infected cases because the duration of PCR detection for COVID-19 is long in children. Second, only three sites were included in the study, which limits the generalizability to other settings. Third, as mentioned earlier, the study was conducted before the emergence of novel SARS-CoV-2 variants, which have increased transmissibility compared to the original strain. Fourth, it is well known that COVID-19 can lead to a myriad of symptoms, not just respiratory ones, that the exposed children were being monitored for. Finally, adolescents were not included in the analysis and, therefore, the findings should not be extrapolated to this age group.

A targeted strategy of keeping symptomatic children away from school may be effective in preventing COVID-19 transmission, rather than blanket school closures. Allowing schools to remain open has important downstream effects, such as alleviating parents from having to miss work because of homebound children. It appears that the focus should be on adult staff members at preschools and secondary schools, rather than children, to reduce the spread of COVID-19 in these settings. Thus, COVID-19 vaccination of preschool and secondary school staff is strongly encouraged. 


  1. Xie Y, Du D, Karki CB, et al. Revealing the mechanism of SARS-CoV-2 spike protein binding with ACE2. Comput Sci Eng 2020;22:21-29.
  2. Zhou D, Dejnirattisai W, Supasa P, et al. Evidence of escape of SARS-CoV-2 variant B.1.351 from natural and vaccine-induced sera. Cell 2021;S0092-8674(21)00226-9.