A total of 993 publications were retrieved and 16 unique studies were finally included for narrative synthesis ( Figure 1 ): two studies investigating SARS-CoV-2 transmission from SARS-CoV-2 positive children [4,5]; six studies presenting indirect evidence on the potential of SARS-CoV-2 transmission by children [3,6-10]; two studies exploring school outbreaks [5 ,11] and one paediatric case report of tracing close contacts in schools [12]. We also found five studies [13-17], that addressed a relevant research question (ie, proportion of children infected as identified through random or targeted population testing) and we also report results from a large hospital-based study in the UK [18].

Figure 1.  Flowchart summarizing study identification and selection. *One study reported documented cases of SARS-CoV-2 transmission by diagnosed children in school settings.

This rapid evidence review summarises the currently available evidence on the role of children in SARS-CoV-2 transmission. The key messages based on the findings of this review are: (i) Case series and outbreak reports detailing transmission in children are few. Those studies which are available demonstrate that transmission by children is possible but do not quantify the likelihood of transmission in children compared to adults. (ii) There is theoretical evidence that alternative transmission routes such as faeco-oral transmission may pose a higher risk in children. Further investigation is required to confirm whether longer viral shedding times in stools in children pose a higher risk of transmission. (iii) There is little evidence on transmission dynamics in school settings. Given the current paucity of data, further investigation and close monitoring will be essential where schools have re-opened and in settings where schools have remained open. (iv) Children are infected, but perhaps less frequently than adults. However, these studies are limited by small numbers and additional community seroprevalence surveys are needed to confirm the proportion of children infected.

Direct evidence showing children as a source of transmission is scarce and largely based on small studies or studies investigating few paediatric cases. We identified two studies indicating that children can transmit COVID-19 to other children or adults [4,5], however, these studies have a high degree of uncertainty. The early case series of paediatric cases in China [4] (providing evidence on children as a source of adult infection) has been questioned by the Swiss National Science Task Force group [22], who stated that a check of the original data does not confirm the reported transmission from the infant to their parents. For the other school-based study, the authors conclude that it is likely that a pupil was infected by one of two other pupils in a high school environment, but they are not certain due to the difficulty in tracking transmission chains in such a widespread outbreak [5].

While there is lack of direct evidence on the frequency that children transmit the disease, indirect evidence illustrates the potential risk of viral transmission by children. First, there is evidence showing that an infected infant contaminated (with SARS-CoV-2) the surfaces they were in contact with, thus rendering the risk of transmitting the virus to caregivers through indirect contact with fomites [ 6]. This finding reinforces the need for caregivers of children to practice hand hygiene as recommended by the WHO. Second, persistent shedding of SARS-CoV-2 in stools of infected children raises the possibility of faeco-oral transmission. This potential is evidenced by at least three studies, which demonstrated that SARS-CoV-2 may be present in the gastrointestinal tract for a longer duration than viral presence in the respiratory system [7 -9]. Findings from these studies suggest that paediatric patients discharged on the basis of a negative respiratory test may remain a potential source of viral transmission and indicate that further precautions may need to be taken to avoid secondary infection during the convalescent phase. Third, several studies reporting that children are more likely to be asymptomatic or mild symptomatic carriers of SARS-CoV-2 lead to the concern that children may transmit the virus to other groups covertly [2,3]. The possibility of asymptomatic transmission of SARS-CoV-2 has been reported in adults by several studies [20, 21 ], while studies specifically targeting the infectiousness of asymptomatic children are yet to be carried out. Future studies aiming to understand children’s contribution to asymptomatic transmission of SARS-CoV-2 should be given priority, as this will influence the balance of control measures for identification and isolation of children and for tracing and quarantining close contacts.

Few studies have described SARS-CoV-2 transmission in schools. There are two studies that investigated school outbreaks of COVID-19 [5,11 ] and one case report of an infected child attending school without infecting other pupils or staff members [12]. Data from both virus and antibody testing suggest that there is limited evidence to suggest significant spread among children and from children to adults. This is consistent with studies showing the majority of infected children are related to family-cluster outbreaks and showing low rates of infection in children [ 3,23].

Understanding the proportion of SARS-CoV-2 infection in children will help to determine children’s relative contribution to SARS-CoV-2 transmission in the community. Based on the infection rates reported from Iceland, Italy, South Korea, Netherlands, and US [13-17], it seems increasingly likely that there are comparatively fewer children with COVID-19 in the community, particularly younger children under the age of 10. Data from these studies confirm that the percentage of children among the confirmed COVID-19 patients is small, varying from 1% in young children up to 6% in older children. It should be noted that these studies are limited by the small numbers of children tested and the potential of biased non-random sampling. Better seroprevalence studies are therefore needed to understand whether infection rates in the community are truly lower among children. The reason why COVID-19 seems to affect children less often and less severely than adults is not yet fully understood, but it could be partially explained by the relatively fewer opportunities for children to expose themselves to people beyond family members and school mates. Given the relatively small proportion of infections and lower chance of exposure, children are unlikely to have been significant drivers of the epidemic so far, and there is not any evidence yet to indicate they are at higher risk of causing super-spreading events in the community.

There is insufficient evidence to robustly answer the key study question. The absence of conclusive evidence on children’s role in transmission increases the uncertainty in relation to policy decisions on school closures and re-openings. During the COVID-19 pandemic, many countries have taken precautionary measures by closing schools to slow transmission among children. As the rate of infection subsides in some areas, some countries have started re-opening schools, and this further highlights the urgency of obtaining robust data on transmission in children and monitoring the impact re-opening schools have on country-level epidemics. A phased re-introduction of face-to-face learning in schools has started in Taiwan (February), Denmark (April), Norway (April), China (May), France (May) and Germany (May). We are committed to reviewing the literature on this topic regularly as new data emerge and to re-evaluate the conclusions of this review given the rapid pace of ongoing research on COVID-19. These updates will be available online (https://www.ed.ac.uk/usher/uncover).

Children are less likely to suffer severe and critical COVID-19 disease than adults [24], however, a new paediatric multisystem inflammatory syndrome associated with SARS-CoV-2 epidemic has recently been identified in the UK, the US, France, Italy, Spain and Switzerland. A small number of children with diagnosed COVID-19 developed a significant systemic inflammatory response with a higher rate of cardiac involvement, caused by a severe form of Kawasaki-like disease [25]. This condition could be fatal and requires prompt and aggressive medical interventions. This has triggered the release of a new guidance from the Royal College of Paediatrics and Child Health [26]. Research on this topic is currently ongoing (DIAMONDS, ISARIC) and a new study from the British Paediatric Surveillance Unit will be launching soon.

This rapid review has a number of limitations. Despite experienced reviewers undertaking searches, screening and data extraction, due to the tight deadline the literature review and data extraction were done by one person per article so it is possible that some key articles may have been missed. We have not performed quality assessment for the included studies, so this may have biased the results. Many of the included studies are pre-print publications or reports and therefore not peer-reviewed. This review should not replace individual clinical judgement and the sources cited should be checked. The views expressed represent those of the authors and are not a substitute for professional medical advice.

There is very limited evidence on paediatric cases acting as a source of infection, which highlights the importance of obtaining robust data on transmission dynamics in children in future studies. Preliminary results from large targeted, population and school studies suggest that children may be less likely to be infected or infect others. Further seroprevalence studies (powered adequately for the paediatric population), are urgently required to establish whether children are in fact less likely to be infected compared to adults. Faeco-oral transmission appears to pose a higher risk of onward transmission in infected children compared to adults, given the longer faecal shedding time observed in several studies. This may have substantial implications for community spread in day-care centres, schools, and homes and the need for a high level of basic hygiene measures in these settings to limit spread.