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Infectious Diseases

Updated 26 August 2020

Children are silent spreaders of Covid-19 virus, new research suggests

A comprehensive study of Covid-19 paediatric patients paints a different picture to previous research suggesting that children are unlikely to catch or spread SARS-CoV-2.

  • The latest research suggests that children do play a key role in transmitting SARS-CoV-2
  • The study found that children with no symptoms were more contagious than infected, sick adults  
  • With schools due to reopen, strict measures must be in place to curb the spread of the virus

In a comprehensive study of Covid-19 paediatric patients by the Massachusetts General Hospital (MGH) and Mass General Hospital for Children (MGHfC), in the United States, researchers in the study found that children may play a larger role in community transmission of the virus than initially thought.

The research team analysed the viral load, immune response and hyperinflammation in 192 paediatric patients between the ages of 0–22. Their paper was published in the Journal of Pediatrics.

Higher viral load, higher risk of transmission

The risk of transmission of SARS-CoV-2 is higher in the case of infected people with a higher viral load. But to gain a deeper understanding, researchers examined the viral load, expression of the viral receptor, and antibody response in healthy children, children with acute SARS-CoV-2 infection, and a smaller number of children with Multisystem Inflammatory Syndrome in Children (MIS-C).

Formerly called paediatric inflammatory multisystem syndrome (PMS), MIS-C describes a relatively new, multi-organ, systemic infection seen in children several weeks after Covid-19 infection.

High viral load found in infected children

Of the total 192 patients, 49 tested positive for SARS-CoV-2, while an additional 18 were found to have late-onset, Covid-19-related illness.

A significantly higher level of virus was also found in the airways of the infected children, compared to hospitalised adults in ICUs (intensive care units) for Covid-19 treatment.

"I was surprised by the high levels of virus we found in children of all ages, especially in the first two days of infection," said Lael Yonker, MD, director of the MGH Cystic Fibrosis Center and lead author of the study.

"I was not expecting the viral load to be so high. You think of a hospital, and of all of the precautions taken to treat severely ill adults, but the viral loads of these hospitalised patients are significantly lower than a 'healthy child' who is walking around with a high SARS-CoV-2 viral load,” added Yonker.

Findings have implications for the reopening of schools

The study results carry implications for the reopening of schools, daycare centres and other locations with a high density of children, as well as close interaction with teachers and staff members, the researchers note.

Alessio Fasano, MD, director of the Mucosal Immunology and Biology Research Center at MGH and senior author of the paper also commented:

“During this Covid-19 pandemic, we have mainly screened symptomatic subjects, so we have reached the erroneous conclusion that the vast majority of people infected are adults. However, our results show that kids are not protected against this virus. We should not discount children as potential spreaders for this virus."

The researchers agree with the wealth of previous studies that note that children are mostly sheltered from developing severe Covid-19, unlike in the case of adults, but argue that, as asymptomatic (displaying no symptoms) carriers, or carriers with few symptoms attending school, they can still transmit the virus and bring it into their homes.

These findings are a serious matter to consider for families, especially multi-generational families, with vulnerable older adults in the house. 

Professor Glenda Gray, president and CEO of the South African Medical Research Council (SAMRC) and a member of the Ministerial Advisory Committee (MAC) acknowledged earlier this month that many South African households are multi-generational, and advised that steps be taken to "de-risk" the schooling environment as much as possible, in order to combat the risk of infection when schools reopen next week.

Another breakthrough

An additional key breakthrough in the study was the discovery that while younger children who have lower numbers of ACE-2 receptors (the "doors" that allow the virus to enter the body’s cells) than older children and adults, it does not necessarily mean they have a decreased viral load (making them less likely to become infected seriously ill), which scientists suggest is currently the case. 

In fact, the authors wrote that the data show that children can carry a high viral load (leaving them more contagious), irrespective of their susceptibility to developing Covid-19.

Understanding MIS-C

When studying the immune response in MIS-C, they found that complications from the accelerated immune response seen in MIS-C can include severe cardiac problems, shock and acute heart failure.

"This is a severe complication as a result of the immune response to Covid-19 infection, and the number of these patients is growing," said Fasano, who is also a professor of Paediatrics at Harvard Medical School (HMS).

"And, as in adults with these very serious systemic complications, the heart seems to be the favourite organ targeted by post-Covid-19 immune response," added Fasano.

Understanding the above is critical for developing treatment and prevention strategies, including vaccine strategies, note the researchers.

Safe return to school

As part of a safe return-to-school policy, the team advised that schools do not rely on body temperature or symptom monitoring to identify infection cases in the school setting.

Instead, non-pharmaceutical interventions (NPIs), such as physical distancing, face mask-wearing, hand hygiene, and remote and in-person screening, are crucial to curbing the spread of SARS-CoV, they explained.

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

READ | 'Unequivocally, as a paediatrician and a parent, I believe schools should be open' - Prof Glenda Gray

READ | More scientific reasons why children are largely sheltered from Covid-19

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Image: Getty/ Nicolò Campo