Immunity and COVID

Children are often infected by four human coronaviruses (hCoVs) circulating worldwide namely 229E, HKU1, NL63, and OC43. These cause mild upper respiratory tract illnesses among youngsters with clinical symptoms ranging from asymptomatic infection to severe sickness. The emerging COVID-19 infection has also affected the children but they are mostly asymptomatic or have a mild-to-moderate illness. Clinical symptoms and laboratory and radiological abnormalities are less severe among children than in adults. A very rare multisystem inflammatory syndrome in children (MIS-C) was observed in COVID-19 infected population which was responsible for critical illness and some deaths among children.¹

Based on initial data from countries that have reported large outbreaks and widespread community transmission thus far, including China, Italy, Spain and the USA, children under 18 years of age have generally made up approximately 1–2% of the total confirmed COVID-19 cases.²

Factors that may lead to increased severity of COVID infection among adults may include 1) changes in the endothelial damage and clotting function with age; (2) higher density, increased affinity, and different distribution of angiotensin-converting enzyme 2 receptors and transmembrane serine protease 2; (3) pre-existing coronavirus antibodies (including antibody-dependent enhancement) and T cells; (4) immunosenescence and inflammaging, including the effects of chronic cytomegalovirus infection; (5) more chances of comorbidities associated with severe COVID-19 and (6) deficiency in vitamin D.²

Factors that might be leading to less severity of COVID-19 infection among children include (1) differences in innate and adaptive immunity; (2) more frequent recurrent and concurrent infections; (3) pre-existing immunity to coronaviruses; (4) differences in microbiota; (5) higher levels of melatonin; (6) protective off-target effects of live vaccines and (7) lower intensity of exposure to SARS-CoV-2,

ARS-CoV-2 was found in childrens and adults nasopharyngeal swabs, nasopharyngeal aspirates, throat swabs, and lower respiratory samples using PCR technique. Also, it was observed that the viral load were more in respiratory secretions and stool of children. As per the data available, children could be causing more transmission. Some studies revealed that children are less likely to be infected than adults and may not transmit SARS-CoV-2 as adults. 

The initial data from countries like China, Italy, Spain and the USA, report that approximately 1–2% of the total confirmed COVID-19 cases were children under 18 years of age. As per the WHO–China Joint Mission report out of 55,924 confirmed COVID-19 cases, 2.4% were children under 19 years of age, 2.5% of them developing severe and 0.2% developing critical disease. ³

In another study from China, it was disclosed that among 2143 suspected and confirmed paediatric COVID-19 cases, 50.9% of children had mild infections, 38.8% had moderate infection, 4% of children were asymptomatic, 5.9% of cases were severe or critical illness and 0.6% suffered from ARDS or multi-organ dysfunction. Further studies conclude, that infants and children with comorbidities were at greater risk of severe illness compared to older children below 16 years.^4,5

Studies from Italy show that only 1.2% of children under 18 years of age were COVID-19 infected and no deaths occurred 6.

Studies from the USA from 12 February until 2 April 2020 state that 1.7% of children <18 years of age were reported to be infected with COVID-19.⁷

To conclude paediatric patients have comprised approximately 1–2% of all cases reported in different countries experiencing asymptomatic or mild-to-moderate illness. Rare multisystem inflammatory syndrome in children (MIS-C) was observed in some COVID-19 infected children which resulted in critical illness and some deaths. More studies need to be carried out to study the progression of COVID-19 infection among children and develop a safe, effective vaccine against COVID-19 for them, making them free from the fear and burden of this pandemic.

References

1. Nipunie Rajapakse , D. D. Human and novel coronavirus infections in children: a review. Paediatr Int Child Health 2021, 41(1):, 36-55. .
2. Petra Zimmermann, N. C. Why is COVID-19 less severe in children? A review of the proposed mechanisms underlying the age-related difference in severity of SARS-CoV-2 infections. Arch Dis Child 2021, 106:, 429–439.
3. Report of the WHO–China Joint Mission on Coronavirus Disease 2019 (COVID-19). Available from: https://www.who.int/publications-detail/report-of-the-who-china-joint-mission-on-coronavirus-disease-2019-(covid-19) [Google Scholar]
4. Yuanyuan Dong, X. M., Yabin Hu, Xin Qi, Fang Jiang, Zhongyi Jiang, Shilu Tong Epidemiological Characteristics of 2143 Pediatric Patients, With 2019 Coronavirus Disease in China. Pediatrics 2020. doi: 10.1542/peds.2020-0702
5. Zunyou Wu, J. M. M. Coronavirus Disease 2019 (COVID-19) Outbreak in China.  Summary of a Report of 72 314 Cases From the Chinese Center for Disease Control and Prevention, JAMA. 2020, 323(13):, 1239-1242.
6. Edward Livingston, K. B. Coronavirus Disease 2019 (COVID-19) in Italy, JAMA. 2020, 323(14), 1335.
7. Team, C. C.-R. Coronavirus Disease 2019 in Children - United States, February 12-April 2, 2020. MMWR Morb Mortal Wkly Rep 2020, 69(14):, 422-426.  doi: 10.15585/mmwr.mm6914e4.