Inclusion Criteria:
* 1\. Age ≥45 years to 75 years of age 2. Diagnosed with sIBM based on the ENMC IBM Research Diagnostic Criteria 3. Willing and able to comply with clinic visits and study-related procedures. 4. Provide informed consent signed by the study patient or legally acceptable representative.
5\. Able to understand and complete study-related questionnaires. 6. Able to ambulate at least 20 ft/6 meters with or without assistive device Once arising from the chair, the participant may use any walking device, i.e. walker/frame, cane, crutches, or braces. They cannot be supported by another person and cannot use furniture or walls for support.
7\. If female, the subject must be: (a) surgically sterilized via hysterectomy, bilateral oophorectomy, or bilateral tubal ligation. or (b) of childbearing potential and using a birth control method, such as:
•Combined (estrogen and progestogen-containing) hormonal. contraception associated with inhibition of ovulation:
o Oral
* Intravaginal
* Transdermal
* Progestogen-only hormonal contraception associated with inhibition of ovulation:
* Oral
* Injectable
* Implantable
• Intrauterine device
• Intrauterine hormone-releasing system
• Bilateral tubal occlusion
* Vasectomized partner
* Sexual abstinence or of non-childbearing potential (i.e., no menses for ≥12 consecutive months without any other underlying medical cause) The subject must agree to continue using her selected method of birth control with her sexual partner during the study and for 120 days after study completion.
8\. If male, the subject must have had a vasectomy or must use a reliable method of birth control with their partner or maintain total abstinence from sexual intercourse. The subject must agree to continue using his selected method of birth control with his sexual partner during the study and for 120 days after the study completion.
Exclusion Criteria:
* 1\. Other neurological conditions (e.g., hemiplegia post-stroke, Parkinson's Disease) or musculoskeletal conditions (e.g., severe osteoarthritis) causing mobility impairment.
2\. Any known active malignancy 3. Significant illness or history of significant illness that, in the investigator's opinion, may adversely affect the patient's participation in this study.
4\. Any previous treatment with a complement inhibitor 5. History of meningococcal disease 6. No documented meningococcal and pneumococcal vaccination within 5 years prior to screening visit unless vaccination will be administered during the screening period and prior to initiation of study treatment.
7\. Known contraindication to meningococcal (group ACWY conjugate and group B vaccines) and pneumococcal vaccines.
8\. Subject unwilling to receive meningococcal and pneumococcal vaccinations. 9. Patients with screening serum ALT levels \>3×ULN and/or total bilirubin \>2×ULN (unless bilirubin elevation is due to suspected Gilbert's syndrome).
10\. Active or recent systemic infection within 2 weeks prior to Baseline. 11. Pregnant, planning to become pregnant, or lactating female subjects. 12. Treatment with an experimental drug within 30 days or 5 half-lives of the experimental drug.
13\. Participation in another concurrent interventional clinical trial. 14. Subjects with functional and anatomic asplenia 15. Subjects with positive tests for hepatitis B, hepatitis C, or HIV at screening 16. Presence of active or latent tuberculosis 17. Presence of any other form of myositis or myopathy or myositis overlap with other autoimmune diseases 18. Presence of other autoimmune or autoinflammatory diseases
