I asked my doctor yesterday if the shots are effective even though the viruses keep mutating. She said it is still 80% effective even if the strain changes. She also said once she got the flu and could not get out of bed for 3 days.
We take it only because we have a school-going kid.
On the discomfort side, I took the shot in the morning, had pain in the arm for a few hours, but was playing tennis (and serving) in the evening with no pain. Felt tired at night and slept like a log and now absolutely OK.