( CNN) In a fresh spin to the doping tale that threatens to overshadow the Winter Olympics, the International Olympic Committee( IOC) has refused a request for 15 Russian athletes and coaches “cleared of doping” to attend the PyeongChang Games.

The 13 athletes and two coach-and-fours are amongst 28 Russians whose lifetime bans for doping were overturned by the Swiss-based Court of Arbitration for Sport( CAS ) Thursday.

CAS ruled there was insufficient evidence to display they had violated doping regulations during the 2014 Sochi Winter Olympics.

Russian athletes appealing Olympic ban

The evolution of doping in sport