Inclusion Criteria:  Written informed consent/assent obtained prior to any assessment performed Symptomatic SMA diagnosis based on gene mutation analysis with bi-allelic SMN1 mutations (deletion or point mutations) and any copy of SMN2 gene. Age ≤ 24 months of age at time of treatment  3. Weight ≤17 kg at the time of Screening Period 4. Naïve to treatment or have discontinued an approved drug/therapy 5. Up-to date on recommended childhood vaccinations and RSV prophylaxis with palivizumab (also known as Synagis), per local standard of care  Key Exclusion Criteria:  Previous use of OAV101 or any AAV9 gene therapy Participant with history of aspiration pneumonia or signs of aspiration (eg, coughing or sputtering of food) within 4 weeks prior to Screening Participant dependent on gastrostomy feeding tube for 100% of nutritional intake. Anti-AAV9 antibody titer > 1:50 as determined by ligand binding immunoassay at the time of screening Inability to take corticosteroids Concomitant use of immunosuppressive therapy, plasmapheresis, immunomodulators such as adalimumab, or immunosuppressive therapy within 3 months prior to gene replacement therapy (eg, cyclosporine, tacrolimus, methotrexate, rituximab cyclophosphamide, IV immunoglobulin) Hepatic dysfunction (i.e. AST, ALT, bilirubin, GGT or GLDH, ≥ ULN; CTCAE ≥ 1) at Screening (with the exception of isolated AST elevation: in the absence of other liver laboratory abnormalities, isolated AST elevation is not considered exclusionary) Previously treated with nusinersen (Spinraza®) within 4 months prior to Screening Previously treated with risdiplam (EvrysdiTM) within 15 days prior to Screening (washout period of at least 5 half-lives before Screening)