TraCK study says schoolchildren unlikely to transmit SARS-CoV-2

By Dr. Liji Thomas, MDMar 10 2021

Among the many non-pharmaceutical interventions (NPIs) implemented to fight the spread of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), school and college closures have caused immense disruption of educational and economic activity, as one parent or caregiver is forced to remain at home to look after children, rather than leave home to work or even work at home.

The question as to whether this step is really necessary has been a bone of contention. An interesting new preprint research paper posted to the medRxiv* server reports there is little evidence to suggest the rapid transmission of the virus among school children while attending school.

Study: Transmission of SARS-CoV-2 by children attending school. Interim report on an observational, longitudinal sampling study of infected children, contacts, and the environment. Image Credit: Volurol / Shutterstock

This news article was a review of a preliminary scientific report that had not undergone peer-review at the time of publication. Since its initial publication, the scientific report has now been peer reviewed and accepted for publication in a Scientific Journal. Links to the preliminary and peer-reviewed reports are available in the Sources section at the bottom of this article. View Sources

SARS-CoV-2 transmission in children

Children are known to carry many viruses causing respiratory tract infection, including influenza, which leads to their acting as carriers in the community at large. This has led to school closures in the current pandemic as a means of containing viral spread.

Two facts have become evident so far. One is that the severity of COVID-19 is significantly less among children compared to adults. Secondly, contact tracing shows that children are less likely to be infected than adults, even with the UK variant (Variant of Concern B1.1.7), which is known to be far more transmissible than the original strain.

Few studies have directly examined the possibility of SARS-CoV-2 transmission among children and young people at school, and the mechanisms by which the pathogen spreads are also unclear. The current TraCK (Transmission of Coronavirus-19 in Kids) study, therefore, focused on following up a group of children by longitudinal sampling, including identifying infected children, their contacts, and the sampling of their environment.

The study was carried out when all school-age children returned to school, and stringent strategies were in place to limit transmission in schools. Children with a positive test were asked to isolate away from school for two weeks.

Study details

The study covers the months October to December 2020.

All cases of COVID-19 among the identified study population were first listed if they were of school age and had a positive polymerase chain reaction (PCR) test for the virus within 48 hours after having attended school.

These children were then matched to the schools from where cases had been reported. All such cases were then traced, and sampling was commenced for them, as well as among their contacts. The latter were traced at home and school.

All samples were tested for the virus, and additional samples were taken from surfaces and air in schools and at their homes.

Five children participated in the study, and four were still PCR-positive at the beginning of the study. One of these was a contact of an adult in the same household who had SARS-CoV-2 infection.

What were the results?

Despite having attended school within the 48 hours before the positive test, none of the contacts of these children were found to be infected over 28 days of follow-up, either in the same bubble or at school. For small children, the bubble included the whole class, while for secondary schools, it included close contacts only.

School contacts were those of the same school and in the same age group or near the classroom where the infected child sat.

The results showed that schoolchildren did not typically transmit the infection to their classmates at school. Only one cluster of three cases of asymptomatic infection was detected at one school. This occurred among three children in the same class, but one of them was infected by the UK variant.

This cluster was probably not linked to the index case as they had tested positive in earlier tests at the beginning of the study. They were not in contact with the index patient or with their bubble contacts, who were isolated.

Transmission at home

A single case of transmission from one child to another child at home was observed, where both shared a bedroom. Another instance of child-to-adult transmission was observed. These were the only transmission events observed, probably because all children were isolated once they tested positive.

Viral shedding

In this study, infected children showed viral ribonucleic acid (RNA) shedding for up to ten days from the onset of symptoms. The peak of viral shedding appeared to occur around 5-8 days from the earliest symptoms.

Interestingly, two out of three asymptomatic cases showed very low viral loads, at (<20 copies/10 microlitres RNA.

“The low level detected was similar to levels detected in the environmental samples and it is impossible to exclude detection of inert viral RNA that is present transiently in the nasopharynx, rather than an active virus infection.”

In the third asymptomatic case, a repeat test showed a rise in viral load to >4 million copies per swab, with another asymptomatic infection being identified in the same household. The child continued to shed for a week but never displayed any symptoms of infection.

Environmental contamination

Environmental contamination was observed in the case of children who were at home and actively shedding the virus. Laptops, mobile phones, remotes and other electronic devices were most heavily or frequently contaminated, in addition to the children’s hands. These items continued to be contaminated for up to ten days after the child became negative for the virus, in cases with the highest viral loads.

Ari samples were also positive in half of the four symptomatic cases with moderate viral shedding. These came from rooms where the child was playing or talking or had just been in, for up to seven days from the onset of symptoms. Asymptomatic cases were not associated with positive air samples despite heavy viral shedding in one of them.

This was not observed at schools, where the amounts of viral RNA recovered from contaminated surfaces were very low.

Infectious virus was not recovered from any sample.

In the later cases of COVID-19 among children, the UK variant was identified. None of the air samples showed the presence of viral RNA.

What are the implications?

This small study shows that COVID-19 does not seem to be typically transmitted by children within schools. A few infections may occur by random spread, and this may lead to transmission clusters.

Practically, it also demonstrates the superiority of nasal swabs that are more acceptable, certainly, and more productive of results, in children and safer for the healthcare workers involved. Saliva is also a very useful tool for large-scale testing, but allowance must be made for the difficulty of obtaining saliva samples from children with special needs.

Only a sixth of bubble contacts in isolation participated in the study, allowing for the possibility of missing additional transmission events within the bubble. However, other studies in Germany and Norway have shown no secondary transmission.

“The current study demonstrates that the heightened precautions in schools are also preventing large scale transmission of COVID-19 in mainstream school settings.”

Further studies are urgently required to understand how infections spread among school children, especially when the UK variant is responsible for most infections.

Such data as this may shape policies regarding in-person education at all levels of school.

This news article was a review of a preliminary scientific report that had not undergone peer-review at the time of publication. Since its initial publication, the scientific report has now been peer reviewed and accepted for publication in a Scientific Journal. Links to the preliminary and peer-reviewed reports are available in the Sources section at the bottom of this article. View Sources