Flu viruses survive best when humidity is lowest, which usually means winter. And cold viruses may multiply more efficiently when temperatures in nasal cavities (in mice anyway according to one 2015 study) go below 98.6F degrees.
Also, cold weather often forces us indoors, into climate-controlled, low-humidity buildings and close to potentially infected people.
Source: CR Consumer Reports magazine January 2018
IF YOU LIKE THESE POSTS, PLEASE CONSIDER CLICKING THE ABOVE DONATION BUTTON. THANK YOU!