If anything has baffled the medical profession and scientists during the COVID-19 pandemic, it is the role of children in its transmission and their own response to being exposed to the virus. However, recent studies are helping experts to better understand the impact of the virus on the young.
One study, led by University College London (UCL, 2020) found that children and young people appear to be more than 50% less likely to catch SARS-CoV-2 – the virus that causes COVID-19 – than adults. However, it said that ‘evidence remains weak’ on how likely they are to transmit the virus, according to a review of teaching and tracing, and population screening studies, led by UCL.
Researchers, who reviewed policies around tracking and training, and examined population screening studies, said the findings provide evidence on children's susceptibility to COVID-19, and the data will be important for governments making decisions about schools reopening and easing lockdown restrictions.
In the largest study of its kind, researchers undertook a systematic review and meta-analysis of more than 6 000 international studies, to understand how susceptible children are to catching COVID-19 and whether they pass it on to others.
Professor Russell Viner, of UCL Great Ormond Street Institute of Child Health, the lead author of the study, said: ‘There is an increasing amount of data now available on children and COVID-19, and this is the first comprehensive study to carefully review and summarise what we do and do not know about susceptibility and transmission.
‘Our findings show children and young people appear 56% less likely to contract COVID-19 from infected others. Susceptibility is a key part of the chain of infection, and this supports the view that children are likely to play a smaller role in transmitting the virus and proliferating the pandemic, although considerable uncertainty remains.
‘This new data provides essential evidence to governments around the world to inform their decision-making on whether to reopen schools and reduce or end lockdown measures.’
Separate research from Imperial College London, released in June, identified a new and distinct condition in children, thought to be brought on by exposure to COVID-19 but presenting with severe inflammatory symptoms similar to Kawasaki disease (Whittaker et al, 2020).
‘…researchers undertook a systematic review and meta-analysis of more than 6 000 international studies, to understand how susceptible children are to catching COVID-19 and whether they pass it on to others.’
The condition, which the researchers have named ‘paediatric inflammatory multisystem syndrome temporally associated with SARS-CoV-2’ (PIMS-TS), was studied in 58 children admitted to eight hospitals in England.
The study, led by Imperial College Academic Health Science Centre (AHSC) researchers, involved clinicians and academic partners in hospitals across England, including Great Ormond Street Hospital (GOSH) and the Evelina London Children's Hospital, as well the Kawasaki Disease Research Center at the University of California San Diego.
While the condition is believed to be extremely rare, there are concerns of long-lasting coronary damage. Fewer than 200 cases have been reported in England with a range of symptoms and severity.
PIMS-TS appears to be more likely to affect older children than Kawasaki disease – on average 9 years old versus 4 years old respectively – and presents more often with abdominal pains and diarrhoea alongside more common features such as persistent fever. It also appeared to affect a higher proportion of Black and Asian patients.
Blood tests also show different results to Kawasaki, with PIMS-TS patients revealing more markers of inflammation and cardiac enzymes, suggesting it puts the heart under strain.
‘… while children appear less likely to catch the virus from others, once they are infected researchers remain uncertain about how likely children are to pass it on.’
Lead researcher, Professor Michael Levin, from Imperial's Department of Infectious Disease, said: ‘The new disease presents in a number of ways and can have serious complications. However, the more we learn the better prepared we are to intervene and prevent worse outcomes. For example, patients who develop shock and cardiac failure have a different pattern of blood tests that may help to identify the at-risk group for targeted treatment.’
While the team was unable to confirm that PIMS-TS is caused by COVID-19, 45 of the 58 children had evidence of current or past COVID-19 infection. The researchers said the emergence of a new inflammatory condition during a pandemic was unlikely to be a coincidence.
The UCL researchers, meanwhile, screened 6 332 studies which allowed them to identify 18 pieces of research containing useful data. The analysis showed that children and young people aged under 20 had 56% lower odds of catching SARS-CoV-2 from an infected person, compared with adults, aged over 20 years. However, the researchers did not have sufficient data to determine whether children aged under 12 years had a higher or lower susceptibility than teenagers.
Furthermore, while children appear less likely to catch the virus from others, once they are infected researchers remain uncertain about how likely children are to pass it on.
Researchers said their findings suggested that children are likely to play a lesser role in transmission of SARS-CoV-2 at a population level because fewer children are likely to be infected in the first place. However, the study provides no information on the level to which children can transmit the virus once infected.
Professor Viner added: ‘It is well known that children and young people make up a very small percentage of confirmed clinical cases of COVID-19, in most countries, including the UK. Children and teenagers make up an even smaller proportion of severe cases or deaths.
‘However such data about confirmed infection among clinical cases tells us little about susceptibility or transmission – as most children have few, if any, symptoms and therefore many do not present for testing or come to the attention of doctors.
‘To understand susceptibility and transmission it was essential to look at studies which trace and test all the close contacts of those with infection and at studies which screen whole populations for infections and not just those with symptoms.’
Co-author Dr Rosalind Eggo, of London School of Hygiene and Tropical Medicine, said: ‘The available evidence has been brought together in a systematic way to better understand SARS-CoV-2 infections of children.
‘It suggests that children and young people are at lower risk of infection than adults and may therefore play a smaller role in the epidemic.
‘This new evidence will help us better understand the possible effect of school reopening on transmission in schools and in the community.’
This study is co-authored by researchers from UCL, London School of Hygiene and Tropical Medicine, University of Cambridge, University of Exeter, University of Sydney and National Institute for Public Health and the Environment (Bilthoven, The Netherlands).