Why the coronavirus affects children much less severely than adults has become an enduring mystery of the pandemic. The vast majority of children do not get sick; when they do, they usually recover.
The first study to compare the immune response in children with that in adults suggests a reason for children’s relative good fortune. In children, a branch of the immune system that evolved to protect against unfamiliar pathogens rapidly destroys the coronavirus before it wreaks damage on their bodies, according to the research, published this week in Science Translational Medicine. . . .
When the body encounters an unfamiliar pathogen, it responds within hours with a flurry of immune activity, called an innate immune response. The body’s defenders are quickly recruited to the fight and begin releasing signals calling for backup.
Children more often encounter pathogens that are new to their immune systems. Their innate defense is fast and overwhelming.
Over time, as the immune system encounters pathogen after pathogen, it builds up a repertoire of known villains. By the time the body reaches adulthood, it relies on a more sophisticated and specialized system adapted to remembering and fighting specific threats.
So while the adult immune system works better against pathogens the body has seen before, that of children works better against those that have never been seen. And since very few of us (at least in the West) have seen this before, children have an advantage. In fact, if this is right, it seems that the threat posed by Covid-19 falls into a the range of dangers that the child immune system can handle easily but adults cannot, a range that I suspect must be very small.