Mind you, my information is based on what I was told by my health care provider. They did some routine lab work (including the rubella immunity test) and when my results indicated I wasn't immune I asked them why that was, since I had had the vaccine and *two* boosters. The response I got was that there had been some weak vaccine going around a while back. I would never have thought to ask them to check me for rubella immunity, but at least at my clinic they routinely test all women who are thinking of getting pregnant, just in case. (Of course, it turned out I was already pregnant, but we didn't know that at the time.)