They also found that pre-delta (when a lot of the US was getting their primary series) vaccine immunity was more protective against hospitalization with alpha or whatever it was at the time in the US

I’m not sure if there is a good study that can distinguish the change point as due to waning immunity from the vaccines or if it’s because of vaccine escape, or if infection-mediated immunity from delta is just better…

The data I’ve seen from omicron suggest that a primary vaccine series offers about equal protection as infection with delta, FWIW