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 but evidence remains weak on how likely they are to transmit the virus, finds a UCL-led review of test and tracing and population screening studies.
Researchers say the findings, which are awaiting peer review and formal publication, provide further evidence on children’s susceptibility to COVID-19, and the data will be important for governments making decisions about school reopening and easing lockdown restrictions.
In the largest study of its kind, researchers undertook a systematic review* and meta-analysis study, of more than 6,000 international studies, to understand how likely it is that children catch COVID-19 (known as susceptibility) and whether they pass it on to others (known as transmission or infectiousness).
Lead author Professor Russell Viner (UCL Great Ormond Street Institute of Child Health) 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."
In total 6,332 studies were screened, which allowed researchers to identify 18 studies with useful data: nine were contact-tracing studies, eight were population-screening studies and one was a systematic review of small household cluster contact-screening studies.
In conclusion, the analysis showed that children and young people (aged under 18-20 years of age) had 56% lower odds of catching SARS-CoV-2 from an infected person, compared with adults (aged over 20). Researchers did not have sufficient data to examine whether children (under 12s) differed to teenagers in susceptibility.
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 concluded that their findings imply 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 infectivity of children, i.e. 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 only a very small percent 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 we looked 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 as a whole.
"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 (RIVM), Bilthoven, The Netherlands
*A systematic review carefully identifies all the relevant published and unpublished studies, rates them for quality and bias, and a meta-analysis study summarises the findings.