This is true. However, when it is cold the body will relinquish 'energy' to stay warm. Then bodily reserves are taxed. Then, if the body is in that state, when around others, a bacteria and/or virus which another may have, could be spread more easily (ex hand shakes, hugs, any contact or with shared item usage, etc.) - then when one touches their own face, eyes, nose, etc. it may be transferred.