Children are about half as likely as adults to become infected with coronavirus, according to scientists who reviewed data gathered by contact tracing and population screening studies around the world. The study, which will feed into the debate on when to open schools, found that children and young adults under the age of 20 appear 56% less likely to contract the virus than the over-20s, a finding that supports the idea that children are unlikely to play a major role in spreading the disease. “It’s preliminary evidence, but the weight of evidence is clear that children appear to be less susceptible to Sars-Cov-2,” said Russell Viner, a professor of adolescent health at UCL Great Ormond Street Institute of Child Health and a senior author on the review. “The balance of evidence is clearly that children are the safest group to be out in the community. They have the lowest prevalence of infections and the risk of death or severe infection from Covid-19 is exceptionally low in children,” he said. “So for children themselves, the balance of risk is strongly in favour of a return to school given the very clear evidence of harm due to lockdown.” Researchers assessed more than 6,000 recent papers on the pandemic, most of which – like the review itself - have not yet been peer reviewed or formally published in journals, and whittled them down to 18 that contained useful data on children’s susceptibility to the virus. Nine of the papers examined in further detail were contact tracing studies that followed infections from person to person. Eight reported virus and antibody test data and one was a review of studies on household clusters of infections. One of the studies found that in 31 household clusters of Covid-19, only three could be traced back to a child as the person who brought the infection into the home. Another report from Australia undertook contact tracing of all Covid-19 cases in schools in New South Wales over a six-week period from early March. It found that 18 index cases, comprising nine students and nine staff, gave rise to only two further cases among students and none among teachers, though children were being pulled from the schools at the time and awareness of the infection was high. While the UCL-led review suggests that children are more resilient to the infection, the pooled data were not sufficient to confirm whether children spread the infection more or less easily than adults. “In times of uncertainty, what we need to do is mitigate risks,” Viner said. “I would concur very strongly that an effective test and trace mechanism in place is very important to mitigate the uncertainty about transmission from children.” Rosalind Eggo, a co-author on the review and an infectious disease modeller in public health epidemiology at the London School of Hygiene and Tropical Medicine, said the evidence suggested children and young people were at lower risk of infection than adults and “may therefore play a smaller role in the epidemic as a whole”. She added: “This new evidence will help us better understand the possible effect of school reopening on transmission in schools and in the community.” In a draft consultation published on Friday, a group of senior scientists warned that 1 June was too soon for schools to reopen safely and that more time was needed to set up an effective track and trace system to contain future outbreaks. The Independent Sage committee, chaired by the former government chief scientist Sir David King, found the risk of children picking up the virus could be halved if they returned to school two weeks later than ministers were proposing. Delaying until September would reduce the risk still further, the report adds.