About vectors and efficacy.

If you will take a look at the picture above you will see - both vector vaccines are quite weak: 70% and 66%. Russian Sputnik meanwhile has 92% of efficacy. Here is no trick.

AZ and JJ uses adenovirus type 5 for vaccines. So second shot of AZ is quite weak - body already has immunity against type 5 after first shot. Russian Sputnik use 2 vectors in shots: type 5 (first shot) and type 26 (second shot). That why both shots works well "in full" and right now Russian Sputnik is the only vector vaccine with efficacy above 90%. 2 vectors!