Abstract
Introduction: Although safety data demonstrated the efficacy and effectiveness of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) vaccination for all individuals over 6 months of age, including pregnant and breastfeeding individuals, optimal treatment courses for symptomatic pregnant and lactating individuals infected with SARS-CoV-2 remain to be defined. Case Description: A coronavirus disease 2019 (COVID-19)-vaccinated breastfeeding woman received anti-SARS-CoV-2 monoclonal antibody treatment casirivimab-imdevimab 5 days after diagnosis of a symptomatic breakthrough SARS-CoV-2 infection. Results and Conclusions: The patient did not present with obvious defects in innate or adaptive cellular subsets, but compared with controls had minimal maternal antibody response to recommended pregnancy vaccinations including SARS-CoV-2 and tetanus, diphtheria, pertussis (TDaP). The outcome of the monoclonal antibody infusion treatment was favorable as it transiently increased SARS-CoV-2 antibody titers in plasma and human milk compartments.