I have only had flu once in my life and I second @Sister - all I wanted was to die quickly .I have flu injections every year .
Please be aware if you get flu and act quickly your gp can give you a Tamiflu injection or similar which can reduce it’s severity but eventually when stocks of Tamiflu are low they prioritise who it’s available to.
The govt has priority list for free vaccination - asthmatics , over 65 and anyone with a health issue whose immune system makes them vulnerable and I believe those who have had cancer treatment fit that bill.