[jlokier]

No scientific data unfortunately, but this BBC article explains that even though it's the same substance each time, the effect develops further over multiple doses, and goes on to describe what that means using metaphors.

BBC News - Omicron: Why do boosters work if two doses struggle? https://www.bbc.co.uk/news/health-59639973

Excerpt:

"Fortunately for us - while the contents of the syringe may be identical, a booster is not just more of the same for the immune system.

The protection you're left with after the third dose is bigger, broader and more memorable than you had before."