The effect can be strong, actually, for a number of possible reasons. Let me start by saying nobody is 100% positive quite yet, but the response is "much large

The effect can be strong, actually, for a number of possible reasons. Let me start by saying nobody is 100% positive quite yet, but the response is "much larger than expected". I started to write out a long response about b cells and such, but it's easier to read the articles that explain it with prettier pictures then I do: https://www.science.org/doi/10.1126/science.abj2258 https://www.science.org/doi/10.1126/science.abj2258 The short version of mechanism is: When you are infected, your body preemptively guesses at what variants might occur and makes memory b-cells that can recognize them. When you later are vaccinated, it discovers which ones were "right" and generates an impressive response. Beyond that, in some sense, it makes intrinsic sense - your body really does cost-benefit because of how many foreign bodies it has to deal with anyway - it initially treats it like any other infection, does the simplest, least energy thing it will take to get rid of it, and moves on. When it gets "reinfected" later, it tries a lot harder to not have it happen again because the threat seems higher.