Some snake oil salesman in San Francisco.
Small city then. There were always those around, and they still are. Pushing some imaginary treatments right now.
Not a global vaccination efforts. 99.999% people in the world were not vaccinated to any degree, being it by snake oil or not, so this had no effects in the big picture.
Yes, people tried all kind of stuff, it was a desperate time. Most of the treatments were not very helpful, but mostly harmless.
Anyway - this was purportedly serum, not vaccine. That’s a big difference. The first somewhat useful vaccine for flu came in 1938, 20 years later.
I am just flabbergasted by this guy, who blames Spanish Flu deaths on “faulty vaccine” when there was none available. Just stunning!