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Review 1: "Transmission of SARS-CoV-2 by children attending school. Interim report on an observational, longitudinal sampling study of infected children, contacts, and the environment"

Reviewer: Ashley Murphy (Northwestern University ) | 📒📒📒 ◻️◻️

Published onMay 06, 2022
Review 1: "Transmission of SARS-CoV-2 by children attending school. Interim report on an observational, longitudinal sampling study of infected children, contacts, and the environment"
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key-enterThis Pub is a Review of
Transmission of SARS-CoV-2 by children to contacts in schools and households: a prospective cohort and environmental sampling study in London

AbstractBackgroundAssessing transmission of SARS-CoV-2 by children in schools is of critical importance to inform public health action. We assessed frequency of acquisition of SARS-CoV-2 by contacts of children with COVID-19 in schools and households, as well as the amount of virus shed into the air and onto fomites in both settings.MethodsCases of COVID-19 in children in London schools were identified via notification. Weekly sampling for 3-4 weeks and PCR testing for SARS-CoV-2 of immediate classroom contacts (the “bubble”), non-bubble school contacts, and household contacts was undertaken supported by genome sequencing, along with surface and air sampling in the school and home environment.ResultsWithin schools, secondary transmission was not detected in 28 individual bubble contacts, representing 10 distinct bubble classes. Across 8 non-bubble classes, 3/62 pupils tested positive– all three were asymptomatic and tested positive in one setting on the same day, unrelated to the original index case. In contrast, the secondary attack rate in naïve household contacts was 14.3% (5/35) rising to 19.1% (9/47) when considering all household contacts. Environmental contamination with SARS-CoV-2 was rare in schools, regardless of school type; fomite SARS-CoV-2 RNA was identified in 4/189 (2.1%) samples in bubble classrooms, 2/127 (1.6%) samples in non-bubble classrooms, and 5/130 (3.8%) samples in washrooms. This contrasted with fomites in households, where SARS-CoV-2 RNA was identified in 60/248 (24.2%) bedroom samples, 66/241 (27.4%) communal room samples, and 21/188 (11.2%) bathroom samples. Air sampling identified SARS-CoV-2 RNA in just 1/68 (1.5%) of school air samples, compared with 21/85 (24.7%) of air samples taken in homes.SummaryThe low levels of environmental contamination in schools are consistent with low transmission frequency and adequate levels of cleaning and ventilation in schools during the period of study. Secondary transmission in schools was rare. The high frequency of secondary transmission in households associated with evident viral shedding throughout the home suggests a need to improve advice to households with infection in children in order to prevent onward community spread by sibling and adult contacts. The data highlight that transmission from children is very likely to occur when precautions are reduced.

RR:C19 Evidence Scale rating by reviewer:

  • Potentially informative. The main claims made are not strongly justified by the methods and data, but may yield some insight. The results and conclusions of the study may resemble those from the hypothetical ideal study, but there is substantial room for doubt. Decision-makers should consider this evidence only with a thorough understanding of its weaknesses, alongside other evidence and theory. Decision-makers should not consider this actionable, unless the weaknesses are clearly understood and there is other theory and evidence to further support it.



In their recently released article, “Transmission of SARS-CoV-2 by children attending school: Interim report on an observational, longitudinal sampling study of infected children, contacts, and environments,” Cordery et al. present their findings on the transmission of the novel coronavirus (COVID-19) from infected children to others in their school and household environments. In this study, the research team monitored the transmission of the COVID-19 virus from five infected children to children in the infected children’s immediate classroom environments, in children in another classroom at the infected children’s schools, and members of the infected child’s household over 28 days. In addition, researchers monitored the amount of viral COVID-19 RNA found on surfaces and in the air of the infected children’s homes and schools for 28 days. The research team did not detect transmission of the virus among other children in the infected children’s immediate classroom environments. A cluster of 3 asymptomatic children was identified in another classroom at one school, although the authors believe the infected child did not cause these cases. Three adults and one child in the home environments were found to be infected, but two of the adult infections were believed to result from transmission from another source. Based on this evidence, the authors claim that children infrequently transmit the COVID-19 virus within schools, supporting claims made in other studies cited in the article. 

This study provides a thorough and elegant methodology for monitoring COVID-19 transmission to schoolmates and household members, as well as for monitoring the presence of the COVID-19 virus on surfaces and in the air of infected children’s home and school environments. This methodology can be useful in informing future research regarding COVID-19 transmission by children. Furthermore, this study provides useful recommendations on COVID-19 testing protocols for schools that are open or will soon re-open for in-person classes (e.g., nasal swabs appear to be the most effective measure of COVID-19 RNA). However, this study had a very small sample size (n=5, with school contacts at one school choosing not to participate) and very low participation rates (10-15%) of children in the infected child’s immediate classroom environment, as compared to similar studies. As a result, the strength of evidence for the claims this paper makes is potentially informative, meaning that the claims are not strongly supported, but may yield some insight. 

Given the small sample size and limited context provided, readers must be careful not to generalize these findings to all children and school settings. Limited information is provided about the daily sanitation protocols followed within each school and home setting. Furthermore, no information is provided about how well children adhered to school mitigation strategies. Thus, measuring the quantity of the COVID-19 virus on surfaces and in the air could more accurately represent the efficacy of school, and home sanitation protocols than the quantity of the virus left behind in these locations. Furthermore, since 85-90% of children in the infected children’s immediate classroom settings did not participate in this study, these findings do not accurately portray COVID-19 transmission among the children in closest proximity to the infected children. The authors also provide limited demographic information about the infected children, their classmates, or their families, limiting the generalizability of these findings. Overall, this study can provide useful information to inform future study design, but its claims regarding COVID-19 transmission by children, particularly in school settings, should be taken with caution.


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