(Photo by Zeljko Stevanic/Xinhua)

SYDNEY, Feb. 18 (Xinhua) -- A new study has found children tend to develop mild COVID-19 symptoms because their innate immune system is quick to attack the virus.

In a research paper published in Nature Communications, researchers led by the Murdoch Children's Research Institute (MCRI) in Australia, revealed the immune mechanisms that protect children from severe COVID-19 illness.

"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. Melanie Neeland from MCRI.

"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."

In doing so, the research team analysed blood samples from 48 children and 70 adults across 28 Melbourne households infected with or exposed to COVID-19 and monitored their immune responses during the acute phase of infection and up to two months afterwards.

They found COVID-19 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," Neeland said.

"This shows that the innate immune system, our first line of defence against germs, is crucial to prevent severe COVID-19 in children. Importantly, this immune reaction was not replicated among adults in the study."

Meanwhile, the research team found both kids and adults who were exposed to but tested negative for COVID-19, had increased neutrophil numbers to provide a certain level of protection from disease.