Vaccinations against influenza are an important part of effective management of multiple sclerosis (MS).~Ofatumumab is a human anti-CD20 monoclonal antibody (mAb) which depletes B-cells, a component of the immune system. This study investigates if ofatumumab treated patients can have an immune response that may be protective after receiving the influenza vaccine.~There will be a one week screening period to assess eligibility for the trial. All eligible participants will receive an influenza vaccine during the Screening Period prior to the Investigational Period. This study will enroll 66 participants with relapsing multiple sclerosis into three cohorts in multiple centers. Up to 44 of the participants will begin treatment with ofatumumab or will already be receiving commercial ofatumumab. The remaining 22 participants will remain on their Injectable Disease Modifying Therapy (iDMT). There will be 4 weekly visits during the Investigational Period which will last 4 weeks. There will also be an optional, 6 month Extension Period for Cohorts 1 and 2, who received ofatumumab, to further evaluate immune response. Cohort 3 will not enter the Extension Period.
To assess whether participants treated with ofatumumab 20 mg subcutaneous (s.c.) administered once every 4 weeks (q4) can mount an adequate immune response to inactivated influenza vaccine as measured by humoral responses compared to participants on an iDMT.