stock in the covid19 vaccine maker moderna fell 16 wednesday as investors seemed to struggle to value shares that have nearly tripled in value this year moderna ticker mrna shares had an unbelievable run from the beginning of the year through the middle of last week the stock was up more than 300 over that period beating the sp 500 which climbed 18 the ishares biotechnology etf ibb which was up 14 and the spdr sp biotech etf xbi which fell 11