** Shares of drug developer Vaxart VXRT.O rise 81.2% to 71 cents premarket
** Co says its new experimental norovirus vaccine produced significantly stronger immune responses than the original version in an early-stage trial
** VXRT says that the second generation vaccine increased protective antibodies by 141% for one strain of norovirus and 94% for another
** Co claimed that even at lower doses, the new vaccine performed better than VXRT's original version and all vaccines tested were well-tolerated with no serious side effects
** As of last close, VXRT stock down 40.7% YTD
(Reporting by Padmanabhan Ananthan)
((Padmanabhan.Ananthan@thomsonreuters.com))