The emergence of SARS-CoV-2 variants with mutations in the spike protein is raising concerns about the efficacy of infection- or vaccine-induced antibodies . We compared antibody binding and live virus neutralization of sera from naturally infected and Moderna vaccinated individuals against two SARS-CoV-2 variants, B.1 containing the spike mutation D614G and the emerging B.1.351 variant containing additional spike mutations and deletions . Sera from acutely-infected and convalescent COVID-19 patients exhibited a 3-fold reduction in binding antibody titers to the B.1.351 variant receptor binding domain of the spike protein and a 3.5-fold reduction in neutralizing antibody titers against SARS-CoV-2 B.1.351 variant compared to the B.1 variant . Similar results were seen with sera from Moderna vaccinated individuals . Despite reduced antibody titers against the B.1.351 variant, sera from infected and vaccinated individuals containing polyclonal antibodies to the spike protein could still neutralize SARS-CoV-2 B.1.351, suggesting that protective humoral immunity may be retained against this variant.