How Soon After Shingles Are Contracted Are They Contagious. I

How soon after shingles are contracted are they contagious. I had breast cancer, surgery, chemo and radiation. That was in August 2008. In 2011 after ct and bone scans they discovered metastatic disease in the right sternum and rib. I have bee getting CT AND BONE SCANS along with a once a day medication Letrozole (estrogen blocker). Two years ago I decided to get the shingles vaccine to which my oncollegest strong suggested not to have it due to a weakened Immune system. It there some truth to this even with all steps have been stable. My stepson just contacted shingles around his eyes and face. They are coming to visit on Christmas Eve so want to ensure he is not still contagious. Noticed he has something going on so went to clinic were it was diagnosed as Shingles. I really don't want to get it as I am already under stress.