The FDA accepted Merck's ($MRK) application for V503, a next-generation HPV vaccine designed to usurp Gardasil, setting the stage for a near-term approval and some likely blockbusting sales figures. V503 protects against 9 strains of the virus, outstripping Gardasil's four, and analysts estimate the vaccine could pull in $1.9 billion a year at its peak. Unfortunately for Merck, however, V503 is playing something of a zero-sum game, as much of its potential market share will come at Gardasil's expense, and Leerink estimates the old vaccine will drop from last year's $1.8 billion in sales to $525 million by 2018. The drugmaker isn't disclosing when it expects to get a final word from the FDA, but a standard review typically takes a maximum of 10 months from the filing date. Release