Hi KrCmommy522, thanks so much for your response. I understand that anything above 10 mIU/ml indicates immunity, but I'm just trying to understand the huge varying ranges already within the bounds of immunity. I am wondering if the higher numbers (~10,000 - 50,000+ mIU/ml), perhaps, have a longer immunity, versus the lower numbers (~50 mIU/ml - 500 mIU/ml). any thoughts?