There was a very interesting article years ago that said swabs were mainly for placebo and had no affect on microbe injection into sites. By they way alcohol doesn't kill most 'bugs' bleach does and that is why we swab down contaminated areas in the lab with bleach. But don't swab yourself with bleach. If you are concerned, a quick wipe with virtually any soap product is more effective than an alcohol swab. Oh, if you get a sting from injecting into muscle mass, it is often the alcohol on the skin that you are pushing in with the needle. I, for reasons I will not go into, often have to bleed myself, for professional reasons, believe it or not. I never use an alcohol swab, I wash my arm with some soap and water and that's it. Never had an infection in 35 years. When I bleed people I do use a swab as it is expected, bit like the white coat; don't have one of them either, I always wipe the area with a cotton wool swab before I penetrate with the needle because it stops the sting.
This is opinion and not professional advice.