Can you please explain the last bullet or post a link?

"~ long-term immunity is questionable for covid and you can get only two shoots of this type of vaccine in lifetime while maintaining it efficiency"

This suggests some fundamental misunderstanding in how I think about the immune system (which is unsurprising given I have no formal background there), and I think I'd learn a lot of important things from understanding why or how this works.

If it's hard or deep, I'm glad to do long-form reading if you have a link.