A Study to Evaluate the Efficacy and Safety of VIB4920 in Participants With Sjögren’s SyndromeSS

- Diagnosed with SS by meeting the 2016 American College of Rheumatology (ACR)/EULAR Classification Criteria. - Residual salivary gland function as defined by whole stimulated salivary flow > 0.1 mL/min (only for Population 2). - Have an ESSDAI score of >= 5 at screening; (not including the peripheral nervous system, central nervous system, and pulmonary domains) (only for Population 1). - Have an ESSPRI score of >= 5 at screening (only for Population 2). - Have an ESSDAI score of < 5 at screening (only for Population 2). - Positive for either anti-Ro autoantibodies or rheumatoid factor, or both at screening. - Male and female participants who agree to follow protocol defined contraceptive methods. - No active or untreated latent tuberculosis (TB).

- Medical history of confirmed deep venous thrombosis or arterial thromboembolism within 2 years of signing the informed consent form (ICF). - Risk factors for venous thromboembolism or arterial thrombosis, prothrombotic status. - Concomitant polymyositis or dermatomyositis or systemic sclerosis. - Active malignancy or history of malignancy, except in situ carcinoma of the cervix and cutaneous basal cell carcinoma. - Hepatitis B, hepatitis C, or human immunodeficiency virus infection. - More than one episode of herpes zoster and/or an opportunistic infection in the last 12 months. - Active viral, bacterial, or other infections or history of more than 2 infections requiring intravenous antibiotics within 12 months prior to signing the ICF. - Participants with corona virus disease 2019 (COVID-19) infection or who, in the judgment of the investigator, are at unacceptable risk of COVID-19 or its complications. - A documented positive severe acute respiratory syndrome-coronavirus-2 (SARS-CoV-2) test within 2 weeks prior to randomization. - Received live (attenuated) vaccine within the 4 weeks prior to ICF signature. - Treated with any biologic B-cell-depleting therapy within 12 months or other B-cell targeting therapy < 3 months before randomization. - Injectable corticosteroids (including intraarticular) or treatment with > 10 mg/day dose oral prednisone or equivalent within 6 weeks prior to randomization (only for Population 1). - Treated with systemic corticosteroids for indications other than SS, rheumatoid arthritis (RA), and systemic lupus erythematosus (SLE) for more than a total of 2 weeks within 24 weeks prior to screening visit (only for Population 1). - Received previous treatment with anti-CD40L compounds at any time before screening. - Pregnant or lactating or planning to get pregnant during the duration of the study.