Inclusion Criteria:

1. Is at least the legal age of consent for clinical trials when signing the informed consent form
2. Is capable of providing signed informed consent and complying with protocol requirements
3. Agrees to use contraceptive measures consistent with local regulations and measures described in the protocol
4. Meets the following criteria at screening: ACR/EULAR 2016 pSS who met criteria ≤7 years before screening; ESSDAI ≥5; Anti-Ro/SS-A positive; Residual salivary flow (UWSF rate >0 and/or SWSF rate >0.10)

Exclusion Criteria:

1. Known autoimmune disease or any medical condition that, in the investigator's judgment,would interfere with an accurate assessment of clinical symptoms of pSS or puts the participant at undue risk
2. History of malignancy unless considered cured by adequate treatment with no evidence of recurrence for ≥3 years before the first administration of IMP.
3. Adequately treated participants with the following cancers may be included at any time: Basal cell or squamous cell skin cancer; Carcinoma in situ of the cervix; Carcinoma in situ of the breast; Incidental histological finding of prostate cancer (TNM stage T1a or T1b) Clinically significant uncontrolled active acute or chronic bacterial, viral, or fungal infection
4. Positive serum test at screening for an active infection with any of the following: HBV that is indicative of an acute or chronic infection, unless associated with a negative HBsAg or negative HBV DNA test; HCV based on HCV antibody assay unless a negative RNA test is available; HIV based on test results of a CD4 count of <200 cells/mm3 that are associated with an AIDS-defining condition, HIV based on test results of a CD4 count of >200 cells/mm3 not adequately treated with antiviral therapy
5. Clinically significant disease, recent major surgery (within 3 months of screening), or intention to have surgery during the study; or any other medical condition that, in the investigator's opinion, would confound the results of the study or put the participant at undue risk
6. Immunoglobulin G (IgG) levels cannot be below a certain threshold ( 4g/L)
7. Positive covid test at study start
8. Some of the medications such as vaccines with live components or medicines that may be prescribed cannot be taken either shortly before or during this study
9. Current participation in another interventional clinical study or previously participation in an efgartigimod clinical study and treatment with ≥1 dose of IMP
10. Known hypersensitivity to IMP or 1 of its excipients
11. History (within 12 months of screening) of current alcohol, drug, or medication abuse as assessed by the investigator
12. Pregnant or lactating state or intention to become pregnant during the study
13. Secondary Sjögren's syndrome overlap syndromes where another confirmed autoimmune rheumatic or systemic inflammatory condition is the primary diagnosis
14. Chinese traditional medicine with known immunomodulatory action