A Study to Evaluate the Effect of Belimumab on Vaccine Responses in Subjects With Systemic Lupus Erythematosus (SLE)

Key Inclusion Criteria: * Clinical diagnosis of SLE by American College of Rheumatology (ACR) criteria. * Active SLE disease. * Autoantibody-positive. * Have antibodies with titers \>1.0 microgram (mcg)/mL to no more than 9 of the 23 serotypes present in the pneumococcal vaccine. * Have the ability to understand the requirements of the study, provide written informed consent, and comply with the study protocol procedures. Key Exclusion Criteria: * Pregnant or nursing. * Have received any prior treatment with belimumab. * Have received a live vaccine within the past 30 days. * Have received a pneumococcal vaccination with the past 5 years. * Have a history of severe allergic reaction to a vaccine, contrast agents (such as those used for x-rays and CT scans), or biological medicines. * Have required management of an infection or have had infections that keep coming back within the past 60 days. * Hepatitis B: Serologic evidence of Hepatitis B (HB) infection based on the results of testing for HB surface antigen (HBsAg) and anti-HB core antibody (anti-HBc): * Subjects positive for HBsAg are excluded. * Subjects negative for HBsAg but positive for anti-HBc, regardless of anti-HBs antibody status, are excluded. * Hepatitis C: Positive test for Hepatitis C antibody. * Known human immunodeficiency virus (HIV) infection. * Have current drug or alcohol abuse or dependence. * Have a Grade 3/4 immunoglobulin (Ig)G deficiency (IgG level \<400 milligrams \[mg\]/ deciliter \[dL\]) or IgA deficiency (IgA level \<10 mg/dL). * Subjects who have evidence of serious suicide risk including any history of suicidal behavior in the last 6 months and/or suicidal ideation with some intent to act in the last 2 months or who in the investigator's judgment, pose a significant suicide risk.