Investigating immune systems
For much of the pandemic, doctors could only guess why children’s immune systems were so much more successful at rebuffing the coronavirus.
Despite the alarming number of hospitalized children in the recent surge, young people are much less likely to become critically ill. Less than 1% of children diagnosed with COVID-19 are hospitalized and about 0.01% die — rates that haven’t changed in recent months, according to the American Academy of Pediatrics. Most children shrug off the virus with little more than a sniffle.
A growing body of evidence suggests that kids’ innate immune systems usually nip the infection early on, preventing the virus from gaining a foothold and multiplying unchecked, said Dr. Lael Yonker, an assistant professor of pediatrics at Massachusetts General Hospital.
In a series of studies published in the past year, the husband-and-wife team of Drs. Betsy and Kevan Herold found that children have particularly strong mucosal immunity, so called because the key players in this system are not in the blood but in the mucous membranes that line the nose, throat and other parts of the body that frequently encounter germs.
These membranes act like the layered stone walls that protected medieval cities from invaders. They’re made of epithelial cells — these also line many internal organs — which sit side by side with key soldiers in the immune system called dendritic cells and macrophages, said Betsy Herold, chief of the division of pediatric infectious diseases at the Albert Einstein College of Medicine.
Significantly, these cells are covered in proteins — called pattern recognition receptors — that act like sentries, continuously scanning the landscape for anything unusual. When the sentries notice something foreign — like a new virus — they alert cells to begin releasing proteins called interferons, which help coordinate the body’s immune response.
In an August study in Nature Biotechnology, Roland Eils and his colleagues at Germany’s Berlin Institute of Health found that kids’ upper airways are “pre-activated” to fight the novel coronavirus. Their airways are teeming with these sentries, including ones that excel at recognizing the coronavirus.
That allows kids to immediately activate their innate immune system, releasing interferons that help shut down the virus before it can establish a foothold, Eils said.
In comparison, adults have far fewer sentinels on the lookout and take about two days to respond to the virus, Eils said. By that time, the virus may have multiplied exponentially, and the battle becomes much more difficult.