Regarding boosters in Israel, the US, etc.
I'm not sure if that's a good idea. While a lot of folks predicted the very tight 21-day schedule would not lead to an enduring response since it basically works like a giant prime dose, it feels like the right decision at the time since it saved a lot of lives before Alpha arrived.
But now here we are. While the waning in antibody levels would suffice to protect against Alpha or basal B.1 after six months, the other VoCs and VoIs are much more refractory to nAbs. I think it's now clear VE will decline much faster against these variants. If it weren't Delta, it would be Gamma or Beta breaking through.
Of course, it's important to look at protection vs. severe disease, not only vs. infection:
Data from Israel makes it clear that protection vs. severe disease remains almost intact, although it certainly didn't look like the case very early on when the outbreak hadn't reached the unvaccinated. At the same time, the dip in protection from ~ 94% to ~ 88% means twice as many severe breakthrough cases among the elderly. One could of course argue that halving the number of potential hospitalizations and deaths is worth the boosters.
I'm just not sure how high uptake would be in the first place, and anti-vaxxers would obviously have a field with that one. That might lead to people getting discouraged and refusing first doses, to begin with. Not to mention it means developed countries saving more doses instead of sharing them with Africa, etc. where they are sorely needed.
So yeah. Just my thoughts on that one.