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Children's role during the COVID-19 epidemic: what do we know?

Text updated on 2020-10-30

Children can catch the SARS-CoV-2 coronavirus and pass it on to other children and adults. Children seem to transmit it mostly to other children. Some studies show that children are as contaminating as adults while others indicate that they are 2-3 times less contaminating.

Children generally have less severe forms of COVID-19 than adults (see question What are the COVID-19 symptoms in children?), but this does not necessarily imply that children transmit less.

It is difficult from the available data to accurately assess the role of children in the dynamics of the COVID-19 epidemic. Most studies were conducted when schools were closed (confinement, holidays). They are therefore not representative of situations where the virus is actively circulating in the general population and schools are open. In addition, infected children often have few or no symptoms. This leads to an underestimation of the number of children infected (because they are less detected and less tested). See the question Why are the COVID-19 epidemiological data on children difficult to interpret?

What we know

The census of the cases of contamination shows that children of all ages can contract the coronavirus SARS-CoV-2 and transmit it to other children of all ages and to adults. See the question Can my child pass on the COVID-19 ?
Children, whether symptomatic or asymptomatic, have viral loads similar to adults. Symptomatic children under the age of 5 may even have viral loads 10 to 100 times higher than adults.
The first introductions of the SARS-CoV-2 coronavirus in different parts of the world outside Wuhan involved mainly adults: business trips, tourism, workers near airports or interacting with tourists (taxi drivers). During the confinements of March-April 2020, only adults were allowed to travel, explaining the lower contamination rate of children compared to adults. During the same period, in Sweden, where most schools remained open, the rate of positive test results increased first among adults and then among children. Since children are not very symptomatic, it is also possible that some early paediatric contaminations have not been detected.

What has not yet been fully established

Children seem to infect preferentially children their own age. A study of social interactions conducted in Shenzhen and Shanghai in China shows that, as might be expected, individuals generally have more contact within their age group than with others. During confinement, the pattern changes: social interactions are strongly reduced and the correlation between age groups disappears (children do not go to school and parents work at home more often). In the largest epidemiological "tracing" study to date, conducted in India on more than 500,000 people while schools were closed and then opened, it was observed that children mostly infect individuals of their own age. The 0-4 year olds mainly infect the 0-4 year olds and the 5-17 year olds the 5-17 year olds. In addition, the rate of contamination of the same age group is significantly higher among the youngest: 0-4 year olds contaminated an average of 26% of 0-4 year old contact cases, 5-17 year olds contaminated 11% of 5-17 year olds and 18-29 year olds contaminated 7% of 18-29 year olds. This result seems logical: young children cry, blow their noses and do not yet have a developed hygiene. The older we are, the more we talk to each other from a distance, the less we touch each other and the better the hygiene improves.
Under similar living conditions, children and adults could be at similar risk of being infected with the COVID-19virus. In Sweden, where most schools have remained largely open, no significant difference was observed in the proportion of people testing positive at SARS-CoV-2 in mid-June between young people aged 0-19 and adults aged 20-64 (6.8% versus 6.4%). In Israel, the percentage of people who tested positive at SARS-CoV-2 between January and September 2020 was even slightly higher among children than among adults. Children also sometimes seem to act as "super-spreaders": 17 children monitored by the Israeli Ministry of Health infected more than 10 people each. These observations contradict other studies conducted in China, Spain and France, which suggest that children are 2-3 times less contaminated than adults. However, the latter may suffer from biases that underestimate the infection rate of children. See the question Why are the COVID-19 epidemiological data on children difficult to interpret?
Children appear to be as contaminating as adults. The previously cited epidemiological study of 500,000 people in India indicates that children contaminate as much as adults. Another study in South Korea shows that within households, young people aged 10 to 19 years have a similar probability of contaminating another person as adults. This Korean study does not include enough data for 0-9 year olds. These observations contradict other studies that have analyzed fewer cases and suggest that children are 2-3 times less contaminating. However, the latter may suffer from biases that underestimate the rate of contamination by children. See the question Why are the COVID-19 epidemiological data on children difficult to interpret?

As with the rest of the population, many factors are likely to influence the effect of children on the dynamics of the pandemic: intra- and inter-generational social relations, school enrolment rates, class density, mask wearing rates, school activities carried out without masks, number of children per household. It is therefore important that precise analyses are carried out, country by country, taking into account local realities. Moreover, we still lack data to identify possible differences in contagiousness and infection between 0-2 years, 3-6 years and older children. Studies on this issue would make it possible to guide health measures regarding young children and their entourage (family, crèches, nursery schools) in a more detailed manner.

In conclusion, current data suggest that during periods of high virus circulation and school opening, children are as contaminating as adults to those around them and that they are preferentially contaminating their age group. Even if the role of children in the spread of the coronavirus were to prove weaker than that of adults, transmission by children exists and must therefore be limited as much as possible through barrier actions in order to reduce the progression of the epidemic.

Sources

This German study, involving 49 children of 0-10 years old, 78 people of 11-20 years old, and more than 3000 adults of all ages, all tested positive for the coronavirus SARS-CoV-2 between January and April 2020, found that children have a viral load similar to adults, even though they are asymptomatic.

Jones, T. C., Mühlemann, B., Veith, T., Biele, G., Zuchowski, M., Hoffmann, J., ... & Drosten, C. (2020). An analysis of SARS-CoV-2 viral load by patient age. medRxiv.

This study examines COVID-19 individuals with mild to moderate symptomes. Amount of viral RNA detected in nasopharyngeal swabs from children aged from 5 to 17 years old was similar to that of adults. In young children (less than 5 years old), it is 10 to 100 times higher. This study did not analyze asymptomatic children.

Heald-Sargent, T., Muller, W. J., Zheng, X., Rippe, J., Patel, A. B., & Kociolek, L. K. (2020). Age-related differences in nasopharyngeal severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) levels in patients with mild to moderate coronavirus disease 2019 (COVID-19). JAMA pediatrics, 174(9), 902-903.

Analysis of 12 children under 18 years old hospitalized in Seoul between March 8 and April 28, 2020 and tested positive for SARS-CoV-2 (3 asymptomatic and 9 mildly symptomatic). In South Korea, all confirmed cases COVID-19-positive are isolated in hospitals. Initial viral loads (assessed by nasopharyngeal RT-qPCR tests) are slightly higher in the 9 symptomatic children compared to the 3 asymptomatic children. The virus becomes undetectable in saliva after an average of 10 days and after an average of 30 days for nasopharyngeal swabs.

Han, M. S., Seong, M. W., Kim, N., Shin, S., Cho, S. I., Park, H., ... & Choi, E. H. (2020). Viral RNA Load in Mildly Symptomatic and Asymptomatic Children with COVID-19Seoul, South Korea. Emerging infectious diseases, 26(10), 2497-2499.

Analysis of the dynamics of transmission of SARS CoV-2 infection in children as of March 2020, based on observations in China. During the emerging phase of COVID-19, the infection begins with person-to-person transmission in the community, almost exclusively among adults. The virus then spreads to the family and causes intrafamilial transmission, particularly to the elderly and children, who are vulnerable to infection. The authors predict that if the disease continues to spread unchecked (which has not happened in China), the epidemic may explode, and school transmission mixed with wider community spread may occur. At this stage children can become one of the main vectors for the spread of the virus.

Cao, Q., Chen, Y. C., Chen, C. L., & Chiu, C. H. (2020). SARS-CoV-2 infection in children: Transmission dynamics and clinical characteristics. Journal of the Formosan Medical Association, 119(3), 670.

Chinese report of February 2020 indicating that the dozens of children who tested positive at the very beginning of the epidemic were detected by "contact tracing" and not because they had symptoms.

World Health Organization, & World Health Organization. (2020). Report of the WHO-China joint mission on coronavirus disease 2019 (COVID-19). 16-24 February 2020.

A study of 103 cases of COVID-19 contamination possibly work-related in Asia up to April 2020 shows that the occupations most at risk of catching the coronavirus SARS-CoV-2 are, after care givers, bus and taxi drivers and workers in the transport sector.

Lan, F. Y., Wei, C. F., Hsu, Y. T., Christiani, D. C., & Kales, S. N. (2020). Work-related COVID-19 transmission in six Asian countries/areas: A follow-up study. PloS one, 15(5), e0233588.

A study of social interactions between people in Shenzhen and Shanghai in China shows, as might be expected, that individuals generally have more contact with those in the same age group than with others. Confinement greatly reduces social interactions and eliminates this correlation between age groups.

Zhang, J., Litvinova, M., Liang, Y., Wang, Y., Wang, W., Zhao, S., ... & Ajelli, M. (2020). Changes in contact patterns shape the dynamics of the COVID-19 outbreak in China. Science.

Study carried out in the Netherlands during school closure. The analysis of 731 cases of COVID-19 transmission for which the two involved individuals have been identified indicates that individuals generally infect others in their own age group. In the under-20 age group, 31 infected persons were found, 9 of whom were of primary school age (between 4 and 12 years of age) and 23 who were infected "at home" (i.e. by a person with the same postal code). Of these 23 home infections, in 21 cases, the source was between 21 and 46 years older than the infected person, which could indicate an infection between parent and child. The other 2 infections at home occurred between peers. There were 2 infected individuals aged 0 years; the source was not the same postal code and was over 60 years of age. They could have been grandparents, but this was not reported. 54 family homes were examined in detail. For 10 COVID-19 patients under 18 years old, 43 close contacts were recorded and none of them tested positive, indicating 0% of contamination. The number of contaminations involving children is too low to draw conclusions.

De rol van kinderen in de transmissie van SARS-CoV-2. Nederlands Tijdschrift Voor Geneeskunde. June 2020.

In India, the largest contact tracing study (i.e. the identification of people who have been in contact with an infected person) ever conducted in the world for an infectious disease. In south-eastern India, 575,071 people were tested, who were exposed to 84,965 confirmed cases of COVID-19 between March and July 2020, during which time schools were closed and then reopened. 71% of those infected did not infect any of their contacts, while only 8% of those infected were responsible for 60% of new infections. In all age groups, people were more likely to get the coronavirus from someone of their own age. A high prevalence of infection was observed among children who had been in contact with cases of their own age. On average, 0-4 year olds infected 26% of 0-4 year old contact cases, 5-17 year olds infected 11% of 5-17 year olds and 18-29 year olds infected 7% of 18-29 year olds.

Laxminarayan, R., Wahl, B., Dudala, S. R., Gopal, K., Mohan, C., Neelima, S., ... & Lewnard, J. A. (2020). Epidemiology and transmission dynamics of COVID-19 in two Indian states. Science.

Study of COVID-19 contaminations in households in South Korea between January and March 2020. 124 index cases of 10-19 year olds contaminated 18% of their contacts while the 30-39 or 40-49 year olds (1475 index cases) contaminated 12% of their contacts. The study does not include enough 0-9 year-old index cases to estimate the average percentage of contacts they contaminated. There is no mention of whether transmissions via children occurred during or outside of school closure periods.

Park, Y. J., Choe, Y. J., Park, O., Park, S. Y., Kim, Y. M., Kim, J., ... & Lee, J. (2020). Contact tracing during coronavirus disease outbreak, South Korea, 2020. Emerging infectious diseases, 26(10), 2465-2468.

Study of blood samples from outpatient care in Sweden, where most schools remained open. Seroprevalence (the presence of antibodies indicating an infection COVID-19 past) of youth aged 0 to 19 increased from April to early June 2020 to reach values similar to those of adults aged 20 to 64 in mid-June 2020 (6.8% versus 6.4%). Seroprevalence remained lower for people over 65 years old (1.5%), who were more isolated than others.

Public Health Agency of Sweden. Påvisning av anti-kroppar efter genomgången covid-19 i blodprov från öppenvården (delrapport 1).

Extremely detailed Israeli study of children between January and September 2020, before and after the reopening of schools. 677,982 RT-qPCR tests were conducted on children in Israel between January 27 and September 24, 2020. Of these, 8% (55,288) were positive. In comparison, 157,229 out of 2,548,273 (6%) were positive in adults. The National Serological Survey conducted by the Ministry of Health detected a positive rate in children of 7% compared to 2-5% in adult age groups. It is estimated that approximately 50-70% of children infected with SARS-CoV-2 are asymptomatic. The opening of schools is associated with an increase in the rate of positive children and their closure with a decrease. Excluding transmissions caused by adults, children tend to be infected by other children in their own age group. 7 children infected 10 people each, 3 infected 12 people each, and one child infected 24 people.

Israel, Ministry of Health, COVID-19 Report, 18 October 2020.