AbstractNeutralizing antispike monoclonal antibody (mAb) therapies were highly efficacious in preventing coronavirus disease 2019 (COVID‐19) hospitalization. While severe acute respiratory syndrome coronavirus 2 (SARS‐CoV‐2) variants may harbor spike protein mutations conferring reduced in vitro susceptibility to these antibodies, the effect of these mutations on clinical outcomes is not well characterized. We conducted a case–control study of solid organ transplant recipients who received an antispike mAb for treatment of mild‐to‐moderate COVID‐19 and had an available sample from initial COVID‐19 diagnosis for genotypic sequencing. Patients whose SARS‐CoV‐2 isolate had at least one spike codon mutation conferring at least fivefold decreased in vitro susceptibility were classified as resistant. Overall, 9 of 41 patients (22%) had at least one spike codon mutation that confers reduced susceptibility to the antispike mAb used for treatment. Specifically, 9 of 12 patients who received sotrovimab had S371L mutation that was predicted to confer a 9.7‐fold reduced susceptibility. However, among 22 patients who required hospitalization, 5 had virus with resistance mutation. In contrast, among 19 control patients who did not require hospitalization, 4 also had virus‐containing resistance mutations (p > 0.99). In conclusion, spike codon mutations were common, though mutations that conferred a 9.7‐fold reduced susceptibility did not predict subsequent hospitalization after treatment with antispike mAb.