I believe the factors are alleged to be many, including dry air in heated rooms which irritates nasal passages, many people often huddled indoors which contribu

I believe the factors are alleged to be many, including dry air in heated rooms which irritates nasal passages, many people often huddled indoors which contributes to infection spread, and so on. Cold temperatures are, of course, involved in all of those, but very tangentially. (Unless one persistently lives in poor heating conditions, which combined with cold outside would likely take a toll on one’s immune system—from my, non-doctor’s, understanding.)