A Study Describing the Efficacy and Safety of Belimumab Administered in Adult Participants With Early Systemic Lupus Erythematosus (SLE)

SRI4 is defined as greater than or equal to (>=) 4-point reduction from baseline in SLEDAI-2K score and no worsening (increase of less than [<] 0.30 points from baseline) in PGA and no new Easy- British Isles Lupus Assessment Group (BILAG) A organ domain score or 2 new Easy-BILAG B organ domain scores compared with baseline at the time of assessment without participants discontinuing due to lack of efficacy, dying, taking prohibited medications or meeting treatment failure criteria.

LLDAS is defined as Systemic Lupus Erythematosus Disease Activity Index 2000 (SLEDAI-2K) less than or equal to (<=) 4, with no activity in major organ systems (renal, central nervous system, cardiopulmonary, vasculitis, fever) and no new features of lupus disease activity compared with the previous assessment, Physician Global Assessment (PGA) <= 1, with a 7-day average oral prednisone equivalent dose for SLE reasons <=7.5 milligram (mg)/day and stable treatment and without discontinuing due to lack of efficacy, dying, or taking prohibited medications.

A seven-day average oral prednisone equivalent dose <= 5 mg/day at week 52, if oral prednisone equivalent dose is greater than (>) 5 mg/day at baseline without study intervention discontinuation due to lack of efficacy, serious AE, prohibited medication intake, or treatment failure by Week 52.

SFI Flare was defined as a mild/moderate or severe flare according to the modified Safety of Estrogen in Lupus National Assessment Systemic Lupus Erythematosus Disease Activity Index (SELENA-SLEDAI) SLE Flare Index (modified excluded severe flares from the SELENA-SLEDAI flare assessment that were triggered only by an increase in SLEDAI-2K score to >12). Change in SELENA SLEDAI instrument score of greater than 12.

The CLASI is used to assess the cutaneous lesions of SLE and consists of 2 separate scores: the activity score and the damage score. The activity score evaluates erythema, scale/hypertrophy, mucous membrane lesions, recent hair loss, and nonscarring alopecia, measured at 13 anatomical sites on the skin. The total activity score ranges from 0 to 70. Higher scores indicate greater disease activity and severity in SLE.

The FACIT-Fatigue is a 13-item participant-completed questionnaire used to assess the impact of fatigue over the previous 7 days. Item responses range from 0 (Not at All) to 4 (Very Much). The FACIT-Fatigue is scored as the sum of item responses, with range from 0 to 52, where higher scores indicate less fatigue and a better quality of life.

An AE is any untoward medical occurrence in a clinical study participant, temporally associated with the use of a study intervention, whether or not considered related to the study intervention. An SAE is defined as any untoward medical occurrence that, at any dose, meets one or more of the criteria listed: results in death; is life-threatening; requires inpatient hospitalization or prolongation of existing hospitalization; results in persistent or significant disability/incapacity; is a congenital anomaly/birth defect in a participant's offspring; abnormal pregnancy outcomes; is a suspected transmission of any infectious agent via an authorized medicinal product; or other situations as per the Investigator's medical or scientific judgment. AESIs will include hypersensitivity or post-injection systemic reactions, infections of special interest, malignancy, psychiatric events, and fatal events.

DORIS remission is defined as clinical SLEDAI-2K equal to (=) 0 (excluding anti- double stranded deoxyribonucleic acid [dsDNA] and complement); and PGA < 0.5; and prednisone (or equivalent dose) < 5 mg/day on stable anti-malarial (AM), immunosuppressants (ISs) and biologic therapy.

The SDI measures irreversible changes occurring since the diagnosis of SLE. The questionnaire contains 39 items covering 12 different organ systems. Individual ranges for organ systems are ocular: 0-2, neuropsychiatric: 0-6; renal: 0-3; pulmonary: 0-5; cardiovascular: 0-6; peripheral vascular: 0-5; gastrointestinal: 0-5; musculoskeletal: 0-6; skin: 0-3; endocrine (diabetes): 0-1; gonadal: 0-1; and malignancies: 0-2. The SDI score is calculated by summing the individual scores for 12 organ systems and ranges from 0 (no damage) to 45 (increasing disease damage) where higher score indicates increasing disease damage severity.

An AE is any untoward medical occurrence in a clinical study participant, temporally associated with the use of a study intervention, whether or not considered related to the study intervention. An SAE is defined as any untoward medical occurrence that, at any dose, meets one or more of the criteria listed: results in death; is life-threatening; requires inpatient hospitalization or prolongation of existing hospitalization; results in persistent or significant disability/incapacity; is a congenital anomaly/birth defect in a participant's offspring; abnormal pregnancy outcomes; is a suspected transmission of any infectious agent via an authorized medicinal product; or other situations as per the Investigator's medical or scientific judgment. AESIs will include hypersensitivity or post-injection systemic reactions, infections of special interest, malignancy, psychiatric events, and fatal events.