Here is an example of the efficacy of AZ - from the Lancet:

"Vaccine efficacy for the prespecified primary analysis (combining dose groups) against the primary endpoint of COVID-19 occurring more than 14 days after the second dose was 70·4% (95·8% CI 54·8 to 80·6; 30 [0·5%] of 5807 participants in the ChAdOx1 nCoV-19 group vs 101 [1·7%] of 5829 participants in the control group)"

Absolute reduction 1.2% - looks trivial, but in terms of numbers it is 70 vs 30 - I know which group I would prefer to be in. This was early in the pandemic, so the numbers becoming infected was relatively small compared to what ensued. Of course I would also want to be in the group which did not get that rare but grim side effect - Vaccine Induced Immune Thrombosis/Thrombocytopenia.