Merck & Co. has agreed to pay $688 million to settle two shareholder class actions in federal court in Newark claiming it made false and misleading statements about the efficacy of cholesterol-reducing drug Vytorin. The settlement, announced Thursday, includes $215 million for class members in a suit against Merck and $473 million for the class in a suit against Schering-Plough Corp., which merged with Merck in 2009. The suits claimed that the defendants delayed for two years disclosure of clinical trial results involving Vytorin, a combination of the drugs Zetia and simvastatin.