A Multicenter Study to Assess Response to Influenza Vaccine in Multiple Sclerosis Participants Treated With Ofatumumab

Inclusion Criteria: 1. Signed informed consent must be obtained prior to participation in the study 2. Age 18-55 years old 3. Diagnosis of relapsing MS by 2017 revised McDonald criteria 4. Must be willing to comply with the study schedule 5. Planning to receive a 2020-2021, 2021-2022, or 2022-2023 inactivated influenza vaccine 6. Planning to start treatment with ofatumumab or already on commercially prescribed ofatumumab for at least 2 weeks prior to the screening visit Participants in Cohort 3 must fulfill criteria 1-5 above in addition to the following: 7. Participant must currently be receiving iDMT Exclusion Criteria: 1. Already has received the 2020-2021, 2021-2022, or 2022-2023 season influenza vaccine 2. Known hypersensitivity to any component of the influenza vaccine 3. Any safety finding including low IgG and/or low IgM levels requiring an ofatumumab treatment interruption within the 12 weeks immediately prior to Week 0 4. Any major episode of infection requiring hospitalization or treatment with intravenous antibiotics within 4 weeks prior to or oral antibiotics within two weeks prior to Week 0 5. Known clinical diagnosis of influenza infection during the 2020-2021 influenza season prior to starting the study based on investigator's or subject's personal physician's judgement (laboratory report of confirmed influenza infection is not required) 6. Prior treatment with B-cell targeted therapies (e.g., rituximab or ocrelizumab), lymphocyte-trafficking blockers, alemtuzumab, anti-CD4, cladribine, cyclophosphamide, mitoxantrone, azathioprine, mycophenolate mofetil, cyclosporine, methotrexate, total body irradiation, bone marrow transplantation. Treatment with a natalizumab within 6 months of week 0 7. Treatment with an S1P modulator within 60 days prior to Week 0 8. Participants with any known active systemic bacterial, fungal or viral or fungal infections (such as hepatitis, progressive multifocal leukocencephalopathy, COVID-19 or HIV), or known to have acquired immunodeficiency syndrome (AIDS) 9. Participation in another interventional clinical trial within 14 days prior to the screening visit 10. Pregnant or nursing (lactating) women, where pregnancy is defined as the state of a female after conception and until the termination of gestation, confirmed by a positive hCG laboratory test 11. Women of child-bearing potential 12. Patients with a history of Guillain-Barre syndrome within 6 weeks of receiving the influenza vaccination.