Maternal-Neonatal Transfer of SARS CoV-2 IgG Antibodies among Parturient Women Treated with BNT162b2 mRNA Vaccine during Pregnancy

Abstract

Background

The exclusion of pregnant women from COVID-19 mRNA vaccine trials raised hesitancy regarding the benefit of vaccination of pregnant women, hence little is known about the vaccine's efficacy in this population.

Objective

To determine the maternal-neonatal transplacental transfer of SARS CoV-2 antibodies among vaccinated parturient women. A control group of COVID 19 recovered patients was included in order to compare IgG levels between vaccinated and recovered patients.

Study Design

A prospective cohort study in a single tertiary medical center in Israel between February and March 2021; parturient women who had been vaccinated with BNT162B2 mRNA vaccine during pregnancy were included and compared to COVID-19 recovered parturient women. SARS CoV-2 IgG antibodies were measured in maternal and cord sera, dried blood spot samples taken from newborns, and breast-milk samples. The primary outcome was to determine whether neonatal cord and dried blood spot samples were positive for SARS CoV-2 antibodies and to evaluate transfer ratio defined as cord blood IgG divided by maternal IgG levels.

Results

The study included 64 vaccinated parturient women and 11 parturient women who had COVID-19 disease during pregnancy. All maternal blood sera samples and 98.3% of cord blood sera samples were positive for SARS Cov-2 IgG with median concentrations of 26.1 (IQR 22.0;39.7) and 20.2 (IQR 12.7;29.0) respectively. Similarly, 96.4% of neonatal blood spot samples and all breast milk samples were positive for SARS CoV-2 IgG with median concentrations of 11.0 (IQR 7.2;12.8) and 4.9 (IQR 3.8;6.0), respectively. There was a significant positive correlation between maternal serum levels of SARS Cov-2 IgG and cord blood (R=0.483, p=0.0001), neonatal blood spot (R=0.515, p=0.004), and breast milk levels (R=0.396, p=0.005) of SARS CoV-2 IgG. The median placental transfer ratio of SARS-COV-2 IgG was 0.77. Comparison of vaccinated with recovered COVID-19 patients revealed significantly higher SARS CoV-2 IgG levels in maternal serum and cord blood among vaccinated women (p<0.0001).

Conclusion(s)

Our study demonstrated efficient transfer of SARS CoV-2 IgG across the placenta from women vaccinated with BNT162b2 mRNA vaccine during pregnancy to their neonates with positive correlation between maternal serum and cord blood antibody concentrations. In addition to maternal protection against COVID-19, the vaccine may also provide neonatal humoral immunity.