I was diagnosed with vasculitis 15 months ago..i had a 6 month course of chemo and have been taking various tablets including immune suppressants to control the vasculitis. ...i have been double jabbed earlier this year....how much immunity do i have?

It depends on the immunosuppressive medication you took at the time of the vaccination. If just Prednisone, chance immunity is probably above 50% at your age. But if you are taking stronger medication such as Mycophenolate, chance of producing antibody is likely less than 30%. I think you are a candidate for a third shot regardless of the immunosuppressive med you are taking at this time.

FDA just approved a booster shot for immunosuppressed individuals in US on increasing evidence for limited/ non lasting immunity in such individuals. Otherwise it is impossible to estimate immunity in individuals affected by autoimmune diseases and on immunosuppressants without specific tests.