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 between immunoglobin (Ig) G antibody levels and time was studied using analysis of variance. The relationship between maternal and cord blood IgG levels and between IgG placental transfer (neonatal/maternal) ratio and time was studied using Pearson correlation analysis and linear regression. The study was approved by the Weill Cornell Medicine Institutional Review Board.

RESULTS

By the time of delivery, 55 pregnant women had received one dose of an mRNA vaccine and 67 had received both vaccine doses. Eighty-five women received the Pfizer-BioNTech vaccine, and 37 women received the Moderna vaccine. All women tested negative for SARS-CoV-2 infection using reverse-transcriptase polymerase chain reaction on nasopharyngeal swabs, and all women and neonates were asymptomatic at birth and until time of discharge.