When I say preventative I mean vaccines and such like, I know taking cough mixture won't stop you from getting cough, the same as birds taking certain things will not stop them from becoming ill
But you have to consider a flu jab if you are in a risk band, the same in birds with paramyxo and other ailmemts in a race enviroment, mixing with other birds.
Some fanciers are like hypochondriacs with their birds, yet probably smoke and drink and have a crap diet, but god forbid, not their birds