I'm speculating, but there are a lot of normal, asymptomatic ways in which a virus may be spread. 1. Mucus. Cold weather can trigger a brief runny nose, which

I'm speculating, but there are a lot of normal, asymptomatic ways in which a virus may be spread. 1. Mucus. Cold weather can trigger a brief runny nose, which in turn is easy to wipe on sleeves, arms, or the back of the hand without much/any thought. 2. Saliva. Spittle from speaking is just about impossible to stop.