Children have a highly effective immune response that protects them from severe COVID-19, according to a study from the Murdoch Children’s Research Institute (MCRI). The experts have discovered that specialized cells in a child’s innate immune system rapidly attack the coronavirus and prevent it from spreading.
Prior to this study, it was not yet known why children have mild COVID-19 infections compared to adults, said Dr. Melanie Neeland. The research has identified, for the first time, the immune mechanisms that provide children with protection from the disease.
“Children are less likely to become infected with the virus and up to a third are asymptomatic, which is strikingly different to the higher prevalence and severity observed in children for most other respiratory viruses,” said Dr. Neeland.
“Understanding the underlying age-related differences in the severity of COVID-19 will provide important insights and opportunities for prevention and treatment, both for COVID-19 and possible future pandemics.”
The researchers analyzed blood samples from 48 children and 70 adults across 28 Melbourne households exposed to COVID-19. The immune responses of the household members were monitored during the acute phase of infection and up to two months later.
In one specific case, four family members all tested positive for COVID-19. While the parents exhibited major symptoms of extreme fatigue, headaches, muscle pain, and loss of appetite, their two children had only a mild runny nose.
Dr. Neeland said the study showed that children with COVID-19 have a more robust innate immune response to the virus compared to adults.
“Coronavirus infection in children was characterized by activation of neutrophils, the specialized white blood cell that helps heal damaged tissues and resolves infections, and a reduction in first-responder immune cells such as monocytes, dendritic cells and natural killer cells from the blood.”
“This suggests these infection-fighting immune cells are migrating to infection sites, quickly clearing the virus before it has a chance to really take hold.”
“This shows that the innate immune system, our first line of defense against germs, is crucial to prevent severe COVID-19 in children. Importantly, this immune reaction was not replicated among adults in the study.”
According to Dr. Neeland, children and adults who were exposed to COVID-19 but tested negative for it were also found to have altered immune responses. “Both kids and adults had increased neutrophil numbers, out to seven weeks after exposure to the virus, which could have provided a level of protection from disease.”
The findings confirm a previous MCRI study which found that three children in a Melbourne family developed a similar immune response after prolonged exposure to the coronavirus from their parents.
The researchers stated that although the children had been infected with the coronavirus, they were able to mount an immune response which was so highly effective in stopping the virus from replicating that they never returned a positive test.
The study is published in the journal Nature Communications.