Not exactly your study (CNTO-1275), but, my wife is in ABT-874 study. It also targets IL-12. I.e., for a non-biologist like me, it seems like the same thing.
I heard many different theories on identifying placebo. However, I really don't believe them too much. I'll get to that later after I state why one should stay in the treatment no matter if one is on placebo.
In my opinion, having a chance at receiving a non-placebo treatment for part of the year for something in the forefront of research is better then being on the poorly effective approved treatments.
Furthermore, for many studies, if the treatment looks promising, pharma companies often allow participants to remain on the treatment open label (no placebo) until FDA approval. That means that if one completes a study in a promising drug, one can continue to receive this drug for years before it is approved.
For most diseases, this is not a great benefit. However, with MS, because the approved treatments are not that effective, this is a very important consideration. Receiving a placebo in the short run, may be better in the long run anyway.
But, getting back to placebo identification: There are two versions I heard.
The first, relates to injection site reactions. I.e., "if you are having reactions, it is the real thing." But, in my observation, this doesn't make sense. There are three streams in the first part of the ABT-874 study, (1)placebo every week, (2)placebo and ABT-874 back and forth every week, (3) ABT-874 every week. My wife gets reactions randomly. I.e., she can go a few weeks without reactions, then get two reactions in a row. So, this theory cannot be accurate in this case.
The other theory I heard is to pay attention to how fast the powder dissolves in liquid when one is preparing a shot. I.e., placebo would dissolve faster then the real thing. For us, they all dissolve about equally. So, there is nothing to compare to. Of course, if the theory is wrong and placebo and the real thing dissolve at the same rate, this won't be much help either.