Depends on where you are. A lot of places in the US have been hit especially hard by the flu and rhinovirus this year. Temperature variations where there's a swing of 40 degrees or more also wreak havoc on the airways and cause sinus infections and cold like symptoms. I know I just about never get sick, but I do feel it when we have days of 60 and 70 degree weather intermittently with days of 20 and 30 degree weather.
If anything, Primal has made my immune system stronger.