I've had a look around the internet and have found this info:
This year there are 3 types of vaccines available, one for children from age 2 to year 5 infant school, one for aged 18-65 at risk adults, this is a 4 in 1 jab- protects against 4 different strains of flu, and the last vaccine , a 3 in 1 jab is for 65 and over, which includes the over 75 age group. The 3 in 1 has a compound in it that should help trigger an immune reaction to the flu virus...... important because the older you get, the slower your immune system is.
Just one point, the vaccines do not stop you getting the flu, they help your body to build up an immune resistance, so that should you get the flu, it should not be as bad or as debilitating as it would be without the jab.
Hope this helps you to make the decision to have the jab.