Can children catch COVID-19?
Infection with COVID-19 has been reported in all age groups, including infants, children and young adults. Even so, studies consistently indicate that children under the age of 18 make up only around 2% of total cases worldwide.
One explanation for these low numbers is that, because children often experience milder symptoms than adults, they are less likely to be tested (see below). However, data from countries that have conducted widespread community testing for the virus suggest that children may also be less likely to be infected in the first place. In South Korea, children younger than nine years accounted for just 1% of laboratory-confirmed cases of COVID-19, whereas children aged between ten and 19 accounted for 5.2% of cases. In Iceland, young children were less likely to test positive for SARS-CoV-2 than adolescents or adults, and no cases were found in children under ten years old in random population screening. Similarly, no cases were found among 374 children under ten years old tested for virus in the Italian town of Vò, where 2.4% of people of all ages were found to be infected.
Studies that have traced the contacts of infected people in Guangzhou and Wuhan/Shanghai, China, and in Japan also suggest that children are less likely than adults to test positive for the virus following exposure to an infected person – although one study from Shenzhen, China, suggested that they were equally susceptible to infection. Among the first 150,000 confirmed cases of COVID-19 in the United States, only 1.7% occurred in children under 18 years old, whereas children make up 22% of the whole population.
Childhood COVID-19 infections tend to be milder
Children’s symptoms vary slightly from those seen in adults and tend to be milder. Cough or fever are observed in only around half of symptomatic children, less often than in adults. In contrast, upper respiratory symptoms such as a runny nose or sore throat occur in 30-40% and diarrhoea and/or vomiting are found in around 10% (sometimes this is the only symptom), more often than in adults.
An analysis of confirmed or suspected cases of COVID-19 among children under 18 years old in Hubei province, China, found that 55.4% had mild symptoms or were asymptomatic; only 5.4% of cases in children were severe or critical, compared with 18.5% of adult cases. Although serious illness and death are rare in children, they do occur. In the Hubei study, critical illness was found to develop in 0.4% of laboratory confirmed cases in children. The current reported death rate in children everywhere is 0.01% (equivalent to one in 10,000 cases), considerably lower than all estimates of adult death rates.
Besides this general picture of milder COVID-19 illness in children, there is one potential complication. In late April, the UK’s Paediatric Intensive Care Society issued an urgent alert to GPs following a small rise in the number of critically ill children with overlapping features of toxic shock syndrome (a rare complication of certain bacterial infections) and atypical Kawasaki disease (a disorder in which the walls of the arteries become inflamed). Symptoms include persistent fever, inflammation, and evidence of altered organ function. Some but not all of these children tested positive for COVID-19 at the time of diagnosis of this syndrome; so it is currently unclear if these rare symptoms are being caused by the COVID-19 virus or by some other as yet unknown factor.
What role do children play in transmission?
The fact that children are less likely to show symptoms when infected with SARS-CoV-2 has raised concerns that they may be responsible for covert virus transmission, though there is little direct evidence to suggest that asymptomatic children are playing a major role in spreading the disease. One study which analysed the source of 31 household clusters of COVID-19 in China, Singapore, South Korea, Japan, and Iran found that children were the source of infection in just three of these cases. The China/WHO joint commission, a panel of international experts which investigated the initial COVID-19 outbreak in China, found, by contact tracing, no cases where transmission occurred from a child to an adult. Possibly, the early closure of schools, combined with children’s apparent reduced susceptibility to infection, may have limited transmission from children. However, the absence of coughing in milder or asymptomatic cases may reduce transmission of the virus. Further studies are needed to test this idea.
Although the role children play in transmitting the virus is unclear, evidence consistently demonstrates that children are less likely than adults to acquire infection, and less likely to bring infections into households.
The evidence-base informing decisions about reopening schools
Because no country has implemented school closures as the sole form of social distancing, it is difficult to disentangle their impact from other social distancing measures. One study reviewed the effectiveness of school closures during coronavirus outbreaks, including modelling studies of COVID-19 which predicted that school closures alone would prevent only 2–4% of deaths, much less than other social distancing interventions.
As COVID-19 spreads round the world, data are beginning to emerge but are still limited. An investigation into all documented COVID-19 cases occurring in the Australian state of New South Wales suggested that little transmission occurred within schools: nine teachers and nine school-age children became infected during March and April, but contact tracing revealed that just two of the 735 students and 128 staff with whom they came into contact subsequently developed the illness. However, school attendance was dropping rapidly at this time, and this may have also limited disease spread.
As schools are reopened around the world, careful epidemiological studies of any effects on disease spread will be valuable for all governments that are now considering their options for relaxing COVID-19 restrictions.