These stocks have suffered as the demand for their biggest product -- the coronavirus vaccine -- waned.The S&P 500 is soaring as this bull market roars on, but some stocks, even those that have rebounded in recent times, still are trading at much lower levels than in the past. In fact, two stocks that have dropped in the double digits over the past few years are coronavirus vaccine giants Moderna (MRNA -11.01%) and Pfizer (PFE -2.04%).The two companies have suffered as demand for the vaccine weakened and in ...