Can't remember what the mechanism was without looking it up, but AZ wasn't MRNA, so probably won't carry the same long term risks if you didn't have a bad reaction in the weeks after having it.
The thing we forget now is that people were not considered vaccinated until three weeks or so after they'd had their first shot, so anybody hospitalised post shot in that time frame and needing ICU or dying would have been counted as unvaxxed.
Edit: And when was it that they recommended reducing the cycles for the PCR test, which inevitably brought down the number of cases.