Although the estimation of mortality and morbidity rates caused by pandemics is fraught with difficulty, a trend seems to emerge from current and previous pandemics. Prepubescent and post-pubescent children seem to show a lowered risk for viral infections than the rest of the population.
Has evolution pronounced this age group to be the fittest among us? Is it because we need this demographic to reproduce and perpetuate our species, and prevent us from becoming extinct? And if so, how has evolution protected this demographic from virulent attacks?
Norwegian scientists John Moxnes and Olav Christophersen explain that the immune system is strongly influenced by hormones, including reproductive hormones. They speculate the involution (shrinkage) of the thymus starting at puberty to be one of the reasons why several infectious diseases appear to be less virulent and less lethal when affecting children than they do when they affect adults who have not been exposed to the same infectious agent before.
“The thymic hormones help to stimulate both innate and adaptive immunity, while the combination of larger thymic hormone production and much larger thymic production of T cells in children will make it possible for the ‘rescue forces’ to arrive earlier and be strong and numerous when they arrive,” they write.