How local does a bee need to be before a bee is a local?

Every hayfever season I vow to go and get jabs in the winter. And forget. Last summer someone told me that local honey helps reduce the effects of hayfever by helping you get used to the local pollen. Lovely Mrssenseofplace bought some local honey. Its very tasty. But how local is local? I'm guessing that Bradford may well have very different pollen to our pollen. According to Mr Douglas it doesn't matter much anyway. :( Better forget to have some jabs then.