Board Thread:TV Show Discussion/@comment-5774411-20170822010733/@comment-5014364-20170822011926

The bear wasn't immune to fire, it just took a long time to kill him. If he HAD been a White Walker, he'd have shattered into ice shards when he was stabbed with dragonglass.

No, Viserion is not a White Walker until stated otherwise - apparently you can only make a White Walker from a still-living thing (i.e. a baby).