New Australian research revealed on Friday found that while children's immune systems could help them avoid severe symptoms from COVID-19 infections, the system is less likely to "form memory" of previous infections.
The study, published in the journal Clinical Immunology, was led by the Garvan Institute of Medical Research.
After investigating the T cells and cellular immune responses of the samples, researchers found that, different from adults, children's immune systems had many different naive T cells to fight against SARS-CoV-2 but did not transition into a memory state after they recovered.
"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," said lead author, professor Tri Phan from the Garvan Institute.
Researchers noted that infants start with an immune system blank slate, which has a much higher proportion of naive T cells. As they grow up and are exposed to more viruses, the naive T cells are replaced by memory T cells that are locked into making responses to viruses they have seen before.
T cells are not part of the innate immune system but are part of the adaptive or memory forming part of the immune system, co-author of the study Associate Professor Philip Britton from the Children's Hospital at Westmead told Xinhua.
"The children in our study had predominantly naive T cells. These are T cells randomly generated by the body to be available to respond to pathogens, but they have not previously been selected out for their ability to respond to a particular pathogen."
Researchers said the findings revealed that COVID-19 infection alone in children does not produce the kind of lasting immune response expected, but they anticipate that this could be augmented by vaccines.
"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," Phan said.
The findings also point to why some adults can have a kind of immune overreaction to SARS-CoV-2, as Phan explained that memory T cells recognize only what they've seen before, like a familiar part of the coronavirus that is shared with the common cold coronaviruses.
This may lock the immune system into a misdirected response that is not specific to the virus, causing more severe symptoms as the immune system ramps up to try and fix the problem, he added.