Delta and Delta Plus were less well inhibited (neutralized) by antibodies from infected and vaccinated individuals as compared to the original virus and this likely contributed to the rapid spread of Delta.
It seems to me relatively straightforward that if we would update the vaccine to the spike protein of the delta varient that would help with protecting against it. When talking to people on Facebook I heared strange arguments such as the "vaccine working well" against delta with seems like a really bogus statement given the need for booster shots and many vaccinated spreading the virus. Yes, the vaccine helps but that's no reason not to update it to make it help more.
Can anyone make sense of this?