Before-the-Bell: Chiron Shares Stumble  NEW YORK (Reuters) - Shares of Chiron Corp. &lt;A HREF="http://www.investor.reuters.com/FullQuote.aspx?ticker=CHIR.O target=/stocks/quickinfo/fullquote"&gt;CHIR.O&lt;/A&gt; fell 7  percent before the market open on Friday, a day after the  biopharmaceutical company said it is delaying shipment of its  flu vaccine, Fluvirin, because lots containing 4 million  vaccines do not meet product sterility standards.