** Drugmaker's U.S.-listed shares up 1.3 pct at$46.75 premarket, London-listed up nearly 2 pct
** Cowen & Co analysts say GSK's vaccine to treat shinglesmay be more effective than Merck's
** Glaxo's vaccine HZ/su should be well positioned tocapture market share from Merck's Zostavax if final data from alate-stage study shows HZ/su has better efficacy while treatingolder patients, Cowen says
** Final data from late-stage study expected in H1 2015
** Merck sold $765 mln worth Zostavax worldwide in 2014
** Barclays raised its price target on European drugmakers,including GSK's London-listed stock
** GSK up nearly 2 pct on the LSE
** Through Monday, the U.S. stock had gained 10 pct sinceDec. 18, when GSK reported early data from the late-stage study
Glaxosmithkline (GSK)
