[stillblue]

This sounds as silly as the claim you're refuting.

Can you please provide links to any evidence that it's false? I'm curious.

[blagie]

Best reference is the book "Immune" by Philipp Dettmer. This is discussed in-depth in the chapter "The Hygiene Hypothesis and Old Friends."

[stillblue]

I've read the book. That chapter talks about what kind of environment initially "trains" the immune system. It does not say anything about viruses such as the ones that common cold being ineffective in doing the same. Please be careful when extrapolating from what's written in a pop science book.