American College of Rheumatology (ACR) response is a composite rating scale that includes 7 variables: tender joints count (TJC \[68 joints\]); Swollen joints count (SJC \[66 joints\]); levels of an acute phase reactant (high sensitivity C-reactive protein \[hs-CRP level\]); participant's assessment of pain (measured on 0 \[no pain\]-100 mm \[worst pain\] visual analog scale \[VAS\]); participant's global assessment of disease activity (measured on 0 \[no arthritis activity\]-100 mm \[maximal arthritis activity\] VAS); physician's global assessment of disease activity (measured on 0 \[no arthritis activity\]-100 mm \[maximal arthritis activity\] VAS); participant's assessment of physical function (measured by health assessment questionnaire disability index \[HAQ-DI\], with scoring range of 0 \[better health\] - 3 \[worst health\]). ACR20 response was defined as achieving at least 20% improvement in both TJC and SJC, and at least 20% improvement in at least 3 of the 5 other assessments.

ADA to sarilumab and anti-sarilumab neutralizing antibodies in serum samples were determined using a validated electrochemiluminescence immunoassay method. Percentage of participants with positive ADA during treatment emergent adverse event (TEAE) period (time from first dose of investigational medicinal product \[IMP\] to last dose of IMP + 60 days) was determined. Persistent ADA Response: treatment-emergent ADA detected at 2 or more consecutive sampling time points during the TEAE period, where the first and last ADA positive samples were separated by a period of at least 16 weeks or if the last measured sample was positive. ADA samples were collected prior to IMP administration at Week 0 (baseline), Week 2, 4, 12, 24 and 30.

Adverse event (AE) was defined as any untoward medical occurrence in a participant who received study drug and does not necessary have to have a causal relationship with treatment. All adverse events that occurred from the first dose of the study drug administration up to 60 days after the end of treatment visit were considered as TEAEs. Serious AE (SAE) was an AE resulting in any of the following outcomes or deemed significant for any other reason: death; initial or prolonged inpatient hospitalization; life-threatening experience (immediate risk of dying); persistent or significant disability/incapacity; congenital anomaly or a medically important event. A summary of SAEs, all other non-serious AEs, regardless of causality, are reported in AE section.