As you see in the article, this is a mathematical model which indicates vaccines saved 20,000,000 lives. It is completely unprovable and only serves as a nice sounding talking point.
I also could claim 20,000,000 lives were saved by natural immunity. Or vitamin D from sunshine. Or the placebo effect.
I also could claim 20,000,000 lives were saved by natural immunity. Or vitamin D from sunshine. Or the placebo effect.
All of those mentioned are also not provable.