** Biotechnology firm CSL's CSL.AX shares drop as much as 0.7%

** Morgan Stanley flags a 15% drop in influenza vaccine sales during the first half, pointing to a decline in U.S. vaccination rates for those aged 15 to 64 as key contributor to its sales slump in the country

** Brokerage highlights that U.S. CDC has classified 2024-25 as a high-severity influenza season for all age groups — the first since 2017-18

** Despite the current reduction in sales, Morgan Stanley suggests that severity of current season may support increased vaccination rates for the upcoming season

** Rates stock "overweight" at the price target of A$313/shr

** Stock down 9.9% YTD including current trading session

(Reporting by Kumar Tanishk in Bengaluru)

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