Not sure how effective the flu shot would be against COVID. Honestly I've never taken the flu shot, I rarely get sick. And if I do it's usually only a few really bad days then on the mend again. Always happens though when we have funky changing weather. 15° one day, 40° next. Funny that I was running around Germany most of the time in a t shirt with temperatures ranging 1° to 10° over the 2 weeks and didn't get sick, come back to Aussie weather and within 2 weeks got sick.