Can Zostavax Vaccination Be Taken Before The Age Of Fifty?

Our son, 28 years old, has Down Syndrome and has also been diagnosed with irritable bowel syndrome (IBS) since he was about 9 years old. He had chickenpox when he was five and shingles when he was about 12. We are concerned he could get shingles again, so we would like him to receive the Zostavax vaccination. He is not currently on steroids that lead to suppression of the immune system, but it may be necessary the next time he has a flare of IBS (he has been on prednisone infrequently for past flares and was on 6-MP for a long period although this has been discontinued in the last 2 years). The current recommendation is to not vaccinate under 50 years old, and the reason appears to be cost vs effectiveness (it costs too much vs it won t vaccinate for more than a few years or it won t protect a high enough percentage of people from the disease). Or is there another reason? Our GP and GI doctors have prescribed the vaccination but we can t find anyone who will go outside the CDC/ACIP guidelines and recommendations of age. Can you shed any light on this? Even medical journal citations that discuss this would be good.