A Multicenter, Open-label Study to Assess the Pharmacokinetics, Safety and Efficacy of Certolizumab Pegol in Children and Adolescents With Moderately to Severely Active Polyarticular-course Juvenile Idiopathic Arthritis (JIA) A Multicenter, Open-label Study to Assess the Pharmacokinetics, Safety and Efficacy of Certolizumab ...