Unlike adults, children have largely avoided the deadly wrath of severe COVID-19 symptoms owing to the fact that they have a strong initial ‘innate’ immune reaction that quickly defeats the virus. However, at the same time, their immune system does not remember the virus and does not adapt to it and hence, the risk of reinfection is much higher as compared to adults, a new study has revealed.
The study, led by scientists at the Garvan Institute of Medical Research, Australia, has been published in the journal Clinical Immunology.
Tri Phan, Co-Lead of the Precision Immunology Program at Garvan, lead author of the study, said, “The price that children pay for being so good at getting rid of the virus in the first place is that they don’t have the opportunity to develop ‘adaptive’ memory to protect them the second time they are exposed to the virus.”
“Because children haven’t been exposed to many viruses, their immune system is still ‘naive’. And because they don’t develop memory T cells, they are at risk of getting sick when they become reinfected.”
“With each new infectious episode as they get older, there is a risk of their T cells becoming ‘exhausted’ and ineffective, like the T cells in older people. This is why we think it’s important to vaccinate children,” said Phan.
The scientists explained immune system has two modes. First, innate immune system that acts like a first line of defence, comprising physical barriers such as skin and mucosal surfaces that block viruses from entering. However, it does not distinguish between one type of virus or another.
Then, the second line of defence comprises B and T cells of the adaptive immune system. These cells have specific receptors that can recognise and distinguish different parts of a virus and generate a rapid response to neutralise or limit it.
Now, infants have a high proportion of naive T cells and as they move towards adulthood, they get exposed to to more viruses, the naive T cells are replaced by memory T cells that are locked in to making responses to viruses they have seen before.
“Over time, as you get infections, your immune system becomes more ‘educated’, allowing you to make a faster immune response that’s tightly matched to the viruses that have infected you before,” said Philip Britton, Associate Professor and clinical lead in the study.
“Children’s immune systems move from relying mostly on the innate system, to needing the adaptive system as a backup as they grow older and are unable to clear viruses as rapidly,” said Britton.
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