Our bodies are a complicated, well-oiled machine, and scientists are still trying to understand precisely how we humans work. The miracle of the immune system is one of the most broadly studied areas of medicine, yet much of how it works still remains a mystery.

Here’s a recent discovery you probably haven’t heard about: It seems our immune system is strongly influenced by its earliest encounter with a virus, a phenomenon known as imprinting. Thereafter a child’s immune system will be primed to fight flu viruses with a similar makeup, but may not be as good at recognizing and eliminating pathogens that aren’t so similar.

If a child’s first exposure is to a relatively common strain, they are apt to have greater immunity, and will get the flu less often. But if a child’s first influenza exposure is to a relatively unusual or uncommon strain, their immune system, primed by this uncommon strain, might be less effective at ridding their body of more common flu pathogens, which means they’ll get sick more often. It can also make vaccinations less effective.

This might explain why some people are laid low by a particular illness, whereas others fight off an infection easily while barely getting sick. It’s just one of the many nuances of the immune system that make us all slightly different.

References:

1. Michael. Eisenstein, ‘A shot for all seasons,” Scientific American, Vol. 321(5):54-56