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Schools across the United States are trying out a wide range of strategies to reopen, from all online classes to all in person. File photo: AFP

Coronavirus ‘silent spreaders’: children who seem healthy may be more contagious than sick adults, study says

  • Studies are starting to show how contagious infected children might be, even those with no symptoms
  • Findings could have implications for plans to reopen schools in the middle of a pandemic

A new US study adds to growing evidence that children are not immune to Covid-19 and may even play a larger role in community spread than previously thought.

Researchers at Massachusetts General Hospital and Mass General Hospital for Children found that among 192 children, 49 tested positive for the coronavirus and had significantly higher levels of virus in their airways than hospitalised adults in intensive care units, according to the study published on Thursday in the Journal of Paediatrics.

“Kids are not immune from this infection, and their symptoms don’t correlate with exposure and infection,” said Dr Alessio Fasano, senior author and director of the Mucosal Immunology and Biology Researcher Centre at Massachusetts General Hospital.

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The study comprised of children from ages zero to 22 who arrived at an urgent care clinic or hospital and were suspected of having SARS-CoV-2, the virus that causes Covid-19.

Fasano said some children were brought to these settings after exhibiting symptoms, but others showed no symptoms and were brought in because they had been in contact with an infected person or lived in what was considered a high-risk area.


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“During this Covid-19 pandemic, we mainly screened symptomatic subjects, so we have reached the erroneous conclusion that the vast majority of people infected are adults,” he said. “We should not discount children as potential spreaders for this virus.”

While the number of children who tested positive may come as a shock to some, Dr Roberta DeBiasi, chief of Paediatric Infectious Diseases at Children’s National Hospital in Washington DC, said she’s not surprised based on the patients she’s seen.

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“We know from other respiratory diseases, (children) are known to be vectors in the community,” she said. However, she added this study was unique because it went a step further to quantify viral load.

Study authors challenged the current hypothesis that children were less likely to get sick from Covid-19 because they had fewer virus receptors than adults. The receptor, angiotensin-converting enzyme 2 (ACE2), binds to the coronavirus and enables it to infect healthy cells.

While they found younger children did have fewer receptors, they still carried high levels of virus. This led researchers to think children are more contagious, calling them “silent spreaders” of Covid-19, regardless of their susceptibility to developing infection.

Scientists also discovered only half of the children who tested positive for the disease had a fever, leading experts to question the heavy reliance of non-contact thermal scanners at building entrances.

“How likely are you to pick up every case of Covid? The answer is only 50 per cent of the time,” DeBiasi said. “You still have to put in all those other measures to try to prevent spread (because) children will be missed from screening methods.”

Dr Matthew Heinz from Tucson Medical Centre in Arizona has seen child-to-adult transmission first-hand. He said the study supports anecdotal reports.

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“This is no way inconsistent from what I’ve seen in my own patients and their own families,” he said. “We’re seeing people that are experiencing what the study is confirming for us in real time.”

As the debate for schools to reopen continues, experts worry children may trigger another wave of coronavirus cases if schools solely rely on monitoring symptoms instead of wearing masks and social distancing. They say children could take the virus to multi-generational households and infect those more susceptible to severe illness.

“Kids are a possible source of spreading this virus,” Fasano said. “And this should be taken into account in the planning stages for reopening schools.”