Inclusion Criteria * SMA diagnosis * Aged 2 to \< 18 years * Have had at least four loading doses of nusinersen (Spinraza®) or at least 3 months of treatment with risdiplam (Evrysdi®) at Screening * Must have symptoms of SMA as defined in the protocol Exclusion Criteria: * Anti Adeno Associated Virus Serotype 9 (AAV9) antibody titer using an immunoassay is reported as elevated * Clinically significant abnormalities in test results during screening * Contraindications for lumbar puncture procedure * At Baseline, participants are excluded if they received: * nusinersen (Spinraza®) or * risdiplam (Evrysdi®) within a defined timeframe * Vaccinations 2 weeks prior to administration of OAV101 * Hospitalization for a pulmonary event, or for nutritional support within 2 months prior to Screening or inpatient major surgery planned. * Presence of an infection or febrile illness up to 30 days prior to administration of OAV101 * Requiring invasive ventilation