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Rare severe cases in children

With the exception of babies, severe cases of COVID-19 occur mainly in adults. While they are liable to infection by SARS-CoV-2, children represent only 1,5% of hospitalisations. Unlike what we previously thought, they have a relatively limited role in the spread of SARS-CoV-2. They develop a complete and effective immune response after infection, as do adults, but children’s tissues and organs are not damaged by uncontrolled inflammation. This indicates a better capacity for repair and for infection control, as with other viral infections, and a greater ability to resolve inflammation following primary infection. Amongst hospitalised children, around half are in fragile health (immunosuppression, cancers, lung, cardiac or neurological diseases). Risk factors are unknown in the other half.

However, very early in the pandemic, it was observed that infected children ran the risk of developing symptoms similar to those of Kawasaki syndrome (acute vasculitis was observed in some infants). In these cases, multi-inflammatory syndromes (fever, abdominal pain, myocarditis) and skin rashes (the sudden, brief, appearance of spots or red patches) were observed. In addition, there were gastrointestinal disorders, septic shocks and lymphopenia, grouped together under the term MIS-C (multisystem inflammatory syndrome in children) or PIMS (pediatric inflammatory multisystem syndrome). This corresponds to one case in 100 000 and the syndrome is preceded by several asymptomatic weeks. Currently cases are treated with antibodies and with prednisone (an anti-inflammatory corticosteroid).

Although the precise reasons are unknown, it would seem that these children have elevated levels of auto-antibodies and they show an overexpression of the TCR (T Cell Receptor) TRBV11 repertoire, leading to  selection of “super antigens” that unbalance the  immune system. In the United States, black and Hispanic children are most often affected. It seems that genetic and environmental factors are the cause: for example, Kawasaki syndrome affects Asian children in particular, but not those born in the USA.

There remains the question of vaccinating children. Clinical studies are rare at the moment, due to parental reticence. This is understandable because children have only a slight risk of developing a severe form of the illness. However, vaccination is essential for attaining herd immunity, especially if a more virulent strain emerges. COVID-19 remains a difficult illness to treat, and more thorough studies are crucial in order to understand the genetic, immune system and environmental particularities that will help us to better protect young and old alike.

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