Here's my take. We were warned about the cytokine storm. I believe that's what Israel is experiencing. Those that rec'd the early shots and were exposed to a variant, whether it be Delta or any other, had a severe reaction.
I have a grim outlook on this vax situation. With each new Booster, that produces mutations/variants, then you eventually need another Booster to overcome the new variant, then the latest Booster produces more mutations/variants, on and on, eventually vaxxed people are going to need a Booster daily due to the multitude of variants produced by all the Boosters.
Take note, the current Booster will be out before a year has transpired from the orignial vax?
I'm no scientist but that's my layman's view.