By hand sanitizers, do you mean something other than the isopropyl-gel based hand sanitizers? If not, I would have guessed that would be little different than using a strong soap.

That said, unfortunately there's some element of luck to it. There's compelling evidence that C-section babies have abnormal immune responses and less diverse body flora. And I imagine childhood circumstance affects things too, city vs country affecting the childhood exposure to pathogens and non-pathogens for training.