You laugh but I was a drunk for 20 years and never got the flu. The year I quit I got so sick I thought I was going to die. Anecdotal yes but true.
Same thing happened to me. I got sober in 2004. In 2005 I got hit with a miserable case of the flu. Initially I wondered why it never happened during my drinking career. Then it dawned on me that perhaps I had either been too drunk or hungover to notice.