** Shares of biotechnology giant CSL CSL.AX plunge 17.6% to A$151.350 in early trade, their lowest since mid-February 2018

** Marks biggest intraday fall on record

** Stock also top loser on the benchmark ASX200 .AXJO, which is up 0.4%

** CSL on Tuesday also tapped insider Gordon Naylor as interim CEO following Paul McKenzie's retirement, seeking to calm investor nerves over falling U.S. vaccination uptake and softer profit momentum

** Posts underlying HY net profit after tax attributable of $1.92  billion on a constant‑currency basis, down from $2.11  billion a year earlier

** Stock down 6.4% YTD as of last close

(Reporting by Kumar Tanishk in Bengaluru)

((Tanishk.Kumar@thomsonreuters.com; X: @thatstanishk http://www.x.com/thatstanishk;))