Children, teens may transmit Covid-19 despite high proportion of mild or asymptomatic infections, says study
The coronavirus pandemic has shown a markedly low proportion of cases among children, and evidence currently remains weak on how likely children are to transmit the virus to others. Researchers have now found that symptomatic (those who show symptoms) neonates, children and teenagers shed infectious SARS-CoV-2, the virus that causes Covid-19, indicating that transmission from them is "plausible".
“Children are underrepresented in Covid-19 case numbers. Severity in most children is limited and children do not seem to be major drivers of transmission. However, SARS-CoV-2 infects children of all ages. Despite the high proportion of mild or asymptomatic infections, they should be considered as transmitters unless proven otherwise,” says the research team in their analysis published in Emerging Infectious Diseases, a journal of the US Centers for Disease Control and Prevention (CDC). To address this point, the laboratory of the Geneva University Hospitals and Faculty of Medicine, University of Geneva, Switzerland, used cell culture to assess cultivable SARS-CoV-2 in the upper respiratory tract of 23 children with Covid-19.
In the study, of 638 patients below 16 years of age, 23 (3.6%) tested positive for SARS-CoV-2. It included those who tested positive for Covid-19 during January 25-March 31. The average age was 12 years (range between seven days to 15.9 years). Thirteen patients had an upper respiratory tract infection, two each had fever without source and pneumonia. Samples were collected at an average of two days after the children started showing symptoms. The research team isolated SARS-CoV-2 from 12 (52%) children. “We isolated the virus from children of all ages; the youngest was seven days of age. Median viral load was higher for patients with isolation than for those without isolation. Sex, age, duration of symptoms, clinical diagnosis, symptoms and likelihood of admission did not differ between patients with and without isolation,” says the report.
The analysis shows that viral load — that is, the amount of virus in the body — at diagnosis is comparable to that of adults and that symptomatic children of all ages shed infectious virus in early acute illness, a “prerequisite for further transmission.” According to researchers, isolation of the infectious virus was largely comparable with that of adults, “although two specimens yielded an isolate at lower viral load.”
The research team says that a limitation of their study was the small number of children assessed. They explain that while the “Canton of Geneva was a region severely affected by SARS-CoV-2,” only 23 cases were diagnosed in children at their hospital during the study period. These findings confirm that children are not a major risk group for Covid-19, they add. Citing the small sample size, the researchers also acknowledged that the findings probably underestimate the true rate of infectious virus presence in symptomatic children and said that they cannot comment whether the data reflect the rates of infectious virus shedding in the community.
“SARS-CoV-2 viral load and shedding patterns of the culture-competent virus in 12 symptomatic children resemble those in adults. Therefore, the transmission of SARS-CoV-2 from children is plausible. Considering the relatively low frequency of infected children, even in severely affected areas, biological or other unknown factors could lead to lower transmission in this population. Large serologic investigations and systematic surveillance for acute respiratory diseases and asymptomatic presentations are needed to assess the role of children in this pandemic,” write authors.
A previous study had found that children and teenagers are half as likely to catch Covid-19 than adults aged 20 years and older. However, the analysis by researchers from the London School of Hygiene & Tropical Medicine, UK, did not provide any information on the infectiousness of children — the level to which children can transmit the virus once infected.