Hi Will, yes, I always get a flu shot. And I'm probably due for a pneumonia shot, too. I believe that one is given every 10 years. Since I've been retired, I've hardly been sick, but I do see my blood sugar rise a little during a cold. I figured it was screwed up because I wasn't eating as I normally did.
After looking up online why this happens, I read that when the body is sick, it is under stress and this causes the release of some hormones in order to fight the sickness/stress in the body, but these hormones also interfere with how insulin works, so blood sugar rises. To what extent varies in individuals. I read one account where a woman felt fine but found her blood sugar spike to 195 for no discernable reason, yet days later she came down with pneumonia. It seems her body was already trying to fight off illness for a few days (causing the high blood sugar) but she came down with pneumonia.
Stay well. Wash your hands.