Most children experience mild COVID-19 or show no symptoms, study finds

How do children contribute to COVID transmission?

Most children experience mild COVID-19 disease or do not show any symptoms, according to the latest report from the Imperial College London.

The findings, from report 37 from Imperial's COVID-19 Response Team, describe a systematic literature review of 128 studies published early in the epidemic, 29 of which were considered for meta-analysis which allowed pooled analysis of the data available.

The majority of studies were based on children who were tested as contacts of COVID-19 patients. Most studies were from China, Europe, and North America and there were no eligible studies from low- and middle-income countries, including countries in South America or Africa.

The pooled analysis showed that 3.8 per cent of children experienced severe or critical symptoms. Most children however experienced mild COVID-19 disease and 21 per cent of children were infected but did not show symptoms. The researchers did not find evidence of higher proportion of asymptomatic children compared to proportion of asymptomatic individuals in population-level studies (general population across all ages).

The researchers did not identify any studies designed to assess transmissibility in children and found that susceptibility to infection in children was highly variable across studies.

Infection susceptibility

The researchers conclude that children’s susceptibility to infection and onward transmissibility relative to adults is still unclear and varies widely between studies. They urge that more comprehensive contact-tracing studies, combined with studies that assess whether children carry the antibodies for COVID-19, are needed to quantify children’s transmissibility relative to adults. With children back in schools, results from testing regimes and study protocols that will allow a better understanding of the role of children in this pandemic are critical.

Dr Katy Gaythorpe, of Imperial College London, said: “Our review focused on the role that children may play in the COVID-19 pandemic. We found further evidence that children may experience milder disease, whilst still capable of being infected with SAR-CoV-2. In terms of transmission, the evidence is still sparse; we found evidence of children infecting others, but no studies designed specifically to assess transmissibility. Furthermore, there are a number of case studies where children, infected with SAR-CoV-2, did not go onto infect others despite encountering them. This highlights the importance of continued investigation of one of the outstanding questions around COVID-19: 'how do children contribute to onward transmission?'”

Professor Steven Riley, Professor of Infectious Disease Dynamics at Imperial, explained: "We saw good agreement in the literature that only a small proportion of clinical cases in children become severe. However, we were unable to find any reliable evidence as to how likely children are to be a source of infection compared to adults. This remains an open question that affects the key policy question of whether and when to close schools as an intervention against community transmission."

Dr Sangeeta Bhatia of Imperial College London, said: “We reviewed the evidence on susceptibility of children to SARS-CoV-2, the severity of infection in children, and the transmissibility of children. We find that the evidence supports that children typically experience milder symptoms if they get infected. However, there is not enough evidence to clearly delineate the role that they play in onward transmission. Further studies are needed to address this critical question.”

The full report is available on the Imperial COVID-19 Response Team report website.

The work is presented in the latest report from the WHO Collaborating Centre for Infectious Disease Modelling within the MRC Centre for Global Infectious Disease Analysis, Jameel Institute (J-IDEA), Imperial College London.

Since the emergence of the new coronavirus (COVID-19) in December 2019, the Imperial College COVID-19 Response Team has adopted a policy of immediately sharing research findings on the developing pandemic.