This recent episode of Inside Heath discussed the types and effectiveness of the current flu vaccine in the UK. (The flu segment is at the beginning - 7 minutes.)

The jab has not been very effective for the elderly, but the one given to children has performed better - which protects everyone because children are very effective at spreading flu!

I think the same vaccine is used throughout the northern hemisphere - though here in the UK the 'quadrivalent' (4-strain) variety seems not to have been offered because it's more expensive than the trivalent one.