I've written a piece on 'immune debt' and the many things it might be driven by.
Enjoy, and if you do, please Boost.
https://virologydownunder.com/what-is-immunity-debt/

What is "Immunity Debt"?
Something called "immunity debt" has been in the news quite a bit lately. Most recently, because of what looks like a multicountry Mycoplasma pneumoniae epidemic, but before then, in the buzz around larger or earlier
Virology Down Under