- Correspondence to Dr Alasdair P S Munro, NIHR Southampton Clinical Research Facility and NIHR Southampton Biomedical Research Centre, University Hospital Southampton NHS Foundation Trust, Southampton SO16 6YD, UK;
Since the first reports of SARS-CoV-2 infections in China, doctors, parents and policy-makers have been aware that COVID-19 is ‘not just another respiratory virus’ in children. There is a large discrepancy in case rate and prognosis between young children and older adults that has caught everyone by surprise, and for which the mechanisms remain unknown. As community testing has demonstrated a significant number of children with no or subclinical symptoms,1 key questions needs answering: are there low rates of confirmed infection in children because children are not becoming infected and/or infectious, or is COVID-19 in children usually such a benign upper respiratory illness that does not even cause infants or immune suppressed children to need hospital admission? If children are infected, are they infectious to each other and/or to adults? If so, how long for?
The implications of asymptomatic but potentially infectious children in the community are important. If, as for influenza,2 children are the primary drivers of household SARS-CoV-2 transmission, then silent spread from children who did not alert anyone to their infection could be a serious driver of community transmission. On this presumption but without evidence, school closures were implemented almost ubiquitously around the world to try and halt the potential spread of disease despite early modelling that suggested this would have less impact than most other non-pharmacological interventions.3
Early contact tracing data from Shenzhen, China, appeared to confirm a role for children in transmission. Although apparently presenting with more benign disease or even without symptoms, similar attack rates were found in children and adults in individual households.4 However, the story has subsequently evolved.
Some regions have implemented widespread community testing, such as South Korea and Iceland. Both countries found children were significantly underrepresented. In Iceland, this is true both in targeted testing of high-risk groups compared with adults (6.7% positive compared with 13.7%) and in (invited) population screening, there were no children under 10 found to be positive for SARS-CoV-2 compared with 0.8% of the general population.5 Subsequently, early pre-print data from the town in Vo, Italy, showed similar findings. With 86% of their population screened following the first death in late February, no children under 10 years were found to be positive (compared with 2.6% of the general population).6 This was despite a number of children found to be living with adults who had COVID-19, but where it was not transmitted (or was unable to be detected). Data from contact tracing in Japan demonstrated lower attack rates in children,7 and recent pre-print data from Guangzhou province in China have also demonstrated a much lower secondary attack rate for children than their adult counterparts (OR 0.23 compared with adults >60 years).8…….