That's why people get sick in the winter and not in the summer. Winter, every thing is closed up tight there's no fresh air. Summer, windows are open plenty of fresh air circulating, no sickness.
Except during covid when they told us to keep the windows closed year round. Which made everyone sick. Do you get it yet?

Guess that having a house that is a bit drafty is not so bad after all.

My kitchen window gets opened the most in winter, I have no problem letting in fresh air.