Feds Subpoena Chiron Over Vaccine Debacle  NEW YORK (Reuters) - 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; is being  investigated by a federal grand jury after failing to deliver  its flu vaccine this year because regulators did not consider  it safe.