A multicenter, randomized, controlled study evaluating the efficacy and safety characteristics of Upadacitinib versus Tofacitinib in subjects aged 2 to <16 years with refractory systemic juvenile idiopathic arthritis

INTERVENTION: Control group:Oral Tofacitinib;Experimental group:Oral Upadacitinib; CONDITION: refractory active systemic juvenile idiopathic arthritis PRIMARY OUTCOME: Proportion achieving sJIA ACR 30 response at Week 12;Safety assessment; SECONDARY OUTCOME: sJIA ACR 30/50/70 response at each observation time point; INCLUSION CRITERIA: 1. Informed Consent: The subject and/or legally authorized representative must be able to understand and agree to comply with all protocol requirements, and voluntarily sign an informed consent form approved by an independent ethics committee/institutional review board, indicating the date, prior to the initiation of any screening or study‐specific procedures (and assent forms for minors as required by applicable regulations). 2. Demographics and Laboratory Assessments: (1) Male or female subjects, aged >=2 weeks and <16 years at baseline. (2)Total body weight >10 kg at screening. (3)Laboratory test values at screening, prior to the first dose of the study drug, must meet the following criteria: 1) aspartate aminotransferase (AST) and alanine aminotransferase (ALT) <2.0× the upper limit of normal (ULN) based on age and sex; 2) normal renal function; white blood cell count (WBC) >=3.0×10^9/L; 3) absolute neutrophil count (ANC) >=2.0×10^9/L;