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Coronavirus in children: Are children immune from COVID-19?

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Children can be infected with the new coronavirus, SARS-CoV-2, and become ill with COVID-19. However, they appear to be less susceptible to infection than adults and their symptoms are generally milder. More data are needed to fully understand coronavirus in children and the role children play in transmitting the virus, although early indications suggest that there is less transmission from children than adults.

Are children immune from coronavirus?

COVID-19 infection 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.[1]

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.[2]

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.[3] 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.[4]

Studies that have traced the contacts of infected people in Guangzhou[5] and Wuhan/Shanghai[6], China, and in Japan[7] 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.[8] 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.[9]

COVID-19 in children and young people: Symptoms

Children’s symptoms vary slightly from those seen in adults and tend to be milder.[9] 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.[10]

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.[11] 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.[11] The current reported death rate in children everywhere is 0.01% (equivalent to one in 10,000 cases)[1], considerably lower than all estimates of adult death rates.

Inflammatory syndrome in children

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).[12] 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 multisystem inflammatory 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.[13]

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.[14] 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 infect family members in the household.[10]

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.[15]

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.[16]

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.

From who is at higher risk, to the science behind ‘stay at home’ initiatives, we’re here to share the facts around the current COVID-19 pandemic. Learn more about coronavirus disease control and prevention.

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References

  1. RCPCH Research & Evidence team. COVID-19 - research evidence summaries. Royal College of Paediatrics and Child Health. 2020 May.

  2. COVID-19 National Emergency Response Center, Epidemiology and Case Management Team, Korea Centers for Disease Control and Prevention. Coronavirus Disease-19: The First 7,755 Cases in the Republic of Korea. Osong Public Health and Research Perspectives. 2020 Apr;11(2):85-90. DOI: 10.24171/j.phrp.2020.11.2.05.

  3. Gudbjartsson DF, Helgason A, Jonsson H, et al. Spread of SARS-CoV-2 in the Icelandic Population. The New England Journal of Medicine. 2020 Apr. DOI: 10.1056/NEJMoa2006100.

  4. Lavezzo E, Franchin E, Ciavarella C, et al. Suppression of COVID-19 outbreak in the municipality of Vo, Italy. medRxiv. 2020 Apr. DOI: 10.1101/2020.04.17.20053157.

  5. Jing Q, Liu M, Yuan J, et al. Household Secondary Attack Rate of COVID-19 and Associated Determinants. medRxiv. 2020 Apr. DOI: 10.1101/2020.04.11.20056010.

  6. Zhang J, Litvinova M, Liang Y, et al. Changes in contact patterns shape the dynamics of the COVID-19 outbreak in China. Science. 2020 Apr. DOI: 10.1126/science.abb8001.

  7. Mizumoto K, Omori R, Nishiura H. Age specificity of cases and attack rate of novel coronavirus disease (COVID-19). medRxiv. 2020 Mar. DOI: 10.1101/2020.03.09.20033142.

  8. Bi Q, Wu Y, Mei S, et al. Epidemiology and transmission of COVID-19 in 391 cases and 1286 of their close contacts in Shenzhen, China: a retrospective cohort study. The Lancet Infectious Diseases. 2020 Apr. DOI: 10.1016/S1473-3099(20)30287-5.

  9. CDC COVID-19 Response Team. Coronavirus Disease 2019 in Children - United States, February 12-April 2, 2020. Morbidity and Mortality Weekly Report. 2020 Apr;69(14):422-426. DOI: 10.15585/mmwr.mm6914e4.

  10. Boast A, Munro A, Goldstein H. An evidence summary of Paediatric COVID-19 literature. Don't Forget the Bubbles. 2020 Apr. DOI: 10.31440/DFTB.24063.

  11. Dong Y, Mo X, Hu Y, et al. Epidemiology of COVID-19 Among Children in China. Pediatrics. 2020 Mar. DOI: 10.1542/peds.2020-0702.

  12. PICS Statement: Increased number of reported cases of novel presentation of multi-system inflammatory disease. Paediatric Intensive Care Society. 2020 Apr.

  13. Zhu Y, Bloxham CJ, Hulme KD, et al. Children are unlikely to have been the primary source of household SARS-CoV-2 infections. medRxiv. 2020 Mar. DOI: 10.1101/2020.03.26.20044826.

  14. WHO Team. Report of the WHO-China Joint Mission on Coronavirus Disease 2019 (COVID-19). World Health Organization. 2020 Feb.

  15. Viner RM, Russell SJ, Croker H, et al. School closure and management practices during coronavirus outbreaks including COVID-19: a rapid systematic review. The Lancet Child & Adolescent Health. 2020 May;4(5):397-404. DOI: 10.1016/s2352-4642(20)30095-x.

  16. NCIRS core clinical and epidemiological team, NCIRS interview and home visit team, ICPMR/NSW Pathology, et al. COVID-19 in schools – the experience in NSW. National Centre for Immunisation Research and Surveillance. 2020 Apr.

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