iPhone vibrates on every Viber text message received Even when my viber application is open on a specific discussion, it continues to vibrate on every received message part of the current discussion.

How can I turn off this very annoying feature for Viber discussions ?

or, if not possible, 

How can I turn off the whole Viber notifications vibration ?

I currently use an iPhone 5
It looks like the feedback has been acted upon, and it is now possible to turn off vibrations and sounds while you are using the app already. A very welcome change indeed! (Not sure which version it was implemented in) You can do it by going to "More" tab on Viber, and opening Settings -> Notifications, and turn off "In-App vibrations". See the official Viber documentation here. Excerpt:


  In-App Vibrate
  
  When this option is enabled, you will receive a vibration for every incoming notification.