Cold Air is Dry Air that has a Static Charge
A 2007 article in “Atmospheric Environment”; microbes and allergens that normally float in moist air, will settle and stick to the moisture of our skin and lungs when by contrast the air is dry. This can in turn increase the risk of infection and asthma.
The article goes on to describe several high tech and expensive ionization systems. In the end, the simple solution is to have a humidifier. There is quite a range of options here. While I love my fancy ultrasonic machine, with a bit of maintenance a simple vaporizer does the trick.
So don’t wait for the first evidence of a cold or flu to start looking for this, DO IT NOW!