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Welcome to Impact Factor, your weekly dose of commentary on a new medical study. I'm Dr F. Perry Wilson of the Yale School of Medicine.

It was only 3 years ago when we called the pathogen we now refer to as the coronavirus "nCOV-19." It was, in many ways, more descriptive than what we have today. The little "n" there stood for "novel"—and it was really that little "n" that caused us all the trouble.

You see, coronaviruses themselves were not really new to us. Understudied, perhaps, but with four strains running around the globe at any time giving rise to the common cold, these were viruses our bodies understood.

But the coronavirus discovered in 2019 was novel—not just to the world, but to our own immune systems. It was different enough from its circulating relatives that our immune memory cells failed to recognize it. Instead of acting like a cold, it acted like nothing we had seen before, at least in our lifetime. The story of the pandemic is very much a bildungsroman of our immune systems—a story of how our immunity grew up.

The difference between the start of 2020 and now, when infections with the coronavirus remain common but not as deadly, can be measured in terms of immune education. Some of our immune systems were educated by infection, some by vaccination, and many by both. Head over to Medscape to read the full story.