Study doesn’t show that children are ‘silent super-spreaders’ of coronavirus

“Children are ‘silent super-spreaders’ of coronavirus, scientists warn.”

The Daily Mirror, 20 August 2020

“Coronavirus carrier children ‘silent super-spreaders’ with high viral loads, study finds.”

The Daily Star, 20 August 2020

“Children may be silent super spreaders of Covid-19 because they have high viral loads, a study has claimed.”

Mail Online, 20 August 2020

It has been reported that new research shows children are silent super-spreaders of Covid-19, with implications for the reopening of schools. This is based on findings published in The Journal of Pediatrics about the amount of coronavirus carried by infected children. The stories in the media are generally accurate reports of what the study’s authors say—however, the study does not prove how likely children are to transmit the infection, and some conclusions it draws have been questioned by other scientists. 

The study at Massachusetts General Hospital in America claims to reveal that children “may be a potential source of contagion in the SARS-CoV-2 pandemic in spite of milder disease or lack of symptoms”. It tested the amount (viral load) of SARS-CoV-2 (the virus that causes Covid-19) in infected patients, and found that children “can carry high levels of the virus in their upper airways, particularly early in an acute SARS-CoV-2 infection, yet they display relatively mild or no symptoms.” 

From this, the authors warned that infection control measures such as social distancing, mask use and routine screening for Covid-19 should be introduced in schools, adding: “Without infection control measures such as these, there is significant risk that the pandemic will persist, and children could carry the virus into the home, exposing adults who are at higher risk of developing severe disease.”

However, this study did not test transmissibility. It says it is “likely” that children with high viral loads and symptoms like a cough can transmit the virus “as easily as other viral infections spread by respiratory particles”, but there is no evidence of this presented in the study. 

Professor Adilia Warris, Professor of Paediatric Infectious Diseases at the University of Exeter, told the Science Media Centre that the data in the report “does not support the claim that children are silent spreaders of Covid-19”. 

“The study was not designed to assess risk of transmission. Although a high viral load contributes to the level of contagiousness, it is not the only factor playing a role.”

Dr Simon Clarke, Associate Professor in Cellular Microbiology at the University of Reading, said the study “does not actually demonstrate that children spread the virus”.

“It is already fairly well documented that children do indeed contract the coronavirus causing Covid-19 and that they produce it in large quantities. However it is less clear how much infection they cause in others or how their age may influence that. 

“This study only adds to our understanding of the extent of infection in children, but not the spread of Covid-19. It does not demonstrate, in any way, that children actually spread the virus to adults or other children.”

Just 192 children were enrolled in the study, and only 49 of these were diagnosed with Covid-19. The majority of children in the study—125 patients—did not have Covid-19, and an additional 18 children had confirmed or suspected multisystem inflammatory syndrome, which has been linked to Covid-19. This is a relatively small sample to draw strong conclusions from. 

The study did not control for any patient characteristics that may have affected results. For example, the patients taking part were not all children: participants could be as old as 22, and 13 Covid-19 positive participants (around 27%) were aged between 17 and 22. Although the study said there was “no age correlation with viral load, indicating that infants through to young adults can carry equally high levels of virus”, this does mean it is incorrect to say the findings are solely about children.

Obesity is known to increase the risk of becoming seriously ill with coronavirus, and around 27% of the Covid-19 positive children in this study were obese. There was also no control for other factors, such as the race or economic background of participants, to see if any of these factors may affect viral load.

It is also worth noting that the patients enrolled in the study were those admitted to hospital or urgent care clinics with symptoms of Covid-19 or multisystem inflammatory syndrome. This means the children studied were unwell (or suspected to be) with Covid-19—something that we know is less common in children.

Dr Andrew Preston, Reader in Microbial Pathogenesis at the University of Bath, told the Science Media Centre it was “misleading” to suggest that “children in general will be walking around with high viral loads, when in fact this study was limited to small numbers of children with symptoms.”

“This study is a valuable contribution to the study of Covid-19 in children, but the paper makes some bold claims regarding the role of children as silent spreaders of the Covid-19 virus. Without studies of transmission, and while focused only on symptomatic children who are a minority of the whole children cohort, these claims are largely unfounded.”