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METHODS

Between January 28, 2021, and March 31, 2021, we studied 122 pregnant women with cord blood available at the time of birth at a single academic medical center. Women who self-reported receipt of one or both doses of a messenger RNA (mRNA)–based COVID-19 vaccine and gave birth to a singleton neonate (gestational age between 35 0/7 and 41 2/7 weeks) were included in the study. Semi-quantitative testing for antibodies against S-receptor binding domain 5, 6 was performed on leftover clinical sera of maternal peripheral blood to identify antibodies mounted against the vaccine and on leftover clinical sera of cord blood to study passive immunity. Only women who tested negative for antibodies against the nucleocapsid protein antigen 7 were included to ensure antibodies were not the result of past severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection. The relationship …