It takes about 14 days from having the flu jab for it to become effective. So, if you have actually contracted flu just prior to having it, or during that two weeks, then you will go through all the normal process of having this very nasty illness.
No way would I ever miss out on having this protection. Like others have been having it now for 17 years, sometime my arm is painful for a few days, sometimes just for a couple of days, and. on occasions, not even that.
Pneuomonia jab had several years back, for 'oldies' this is a once only protection, although other people who have this for other medical reasons often need it every five years. And got my shingles jab last year (at last).
Any such protection I can be offered I am very happy to take. Jaxjacky, please be reassured.