Leigh Halfpenny to miss Six Nations start as concussion symptoms persist

• Wales full-back still suffering effects of Samu Kerevi hit• Ospreys centre Ben John retires after repeated head injuriesLeigh Halfpenny is expected to miss at least the first two Six Nations matches after being told by a specialist he is at least three weeks away from a return from concussion.The Wales and Scarlets full-back was concussed against Australia in November – the fourth time in six years. He has not played since and is continuing to show symptoms such as headaches. Related: Wales angry that Samu Kerevi has escaped punishment for late tackle Related: Premiership issues World Rugby…