As far as I know it isn't quantified but the effect is temporary depending on how long it takes for a person's body to acclimatize. The main thing is you don't want to be cold or shivering in a transmissible environment.
Per powdork, and iceman's hypothesis, influenza likes people gathered together in cold dry conditions. There are other viruses, though, that are just as transmissible in warm humid environments.
Sort of related and quantifiable, the relative transmissible-ness of greeting gestures:
Attachment 317582
Maybe just throw a random bird and call it good.