Viral infections and pred

I am on a maintanance dose of Prednisolone 10mg, I am at present slowly reducing back to it after another rocky patch. I have got down to 15mg and seem to be picking up yet another viral infection! I know my immune system is pretty non existant after being on steroids for so long but is there anything at all I can do to help improve this even just a teeny bit?!

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After having several chest infections at the end of last year, i decided to try the old vitamin C trick, and now take 1000mg every day as a minimum, and so far been OK, no colds, or chest infections. Also use a sinus rinse, to help keep the sinuses clear.