What is the optinal timing of maternal SARS-CoV-2 mRNA immunization to maximize transplacental antibody transfer?


      We aimed to assess the optimal timing of maternal SARS-CoV-2 vaccination to maximize transplacental transfer and neonatal levels of SARS-CoV-2 antibodies.

      Study Design

      Maternal and cord blood sera were collected following term delivery after antenatal SARS-CoV-2 BNT162b2 mRNA vaccination. SARS-CoV-2 spike protein (S) and receptor binding domain (RBD)-specific, IgG levels and neutralizing potency were evaluated in maternal and cord blood samples.


      The study cohort consisted of 228 parturients (median age, 31 years; median gestational age, 39.7 weeks): 57 (25.0%) immunized at second trimester (1st dose at 19-26 weeks), 83 (36.4%) immunized at early 3rd trimester (1st dose at 27-31 weeks), and 88 (38.6%) immunized at late 3rd trimester (1st dose at 32-36 weeks). All mother-infant paired sera were positive for anti S- and anti-RBD-specific IgG. Anti-RBD-specific IgG concentrations in neonatal sera were higher following early 3rd trimester vaccination (median 9620 AU/mL) as compared to second (3970 AU/mL) and late 3rd trimester vaccination (6697 AU/mL) (P< 0.001).
      The median placental transfer ratios of anti-S and anti-RBD specific IgG were increased following early 3rd (anti-S ratio:1.3, anti-RBD-specific ratio:2.3) and second trimester vaccination (anti-S ratio:1.5, anti-RBD-specific ratio:2.8) versus late 3rd trimester immunization (anti-S ratio:0.9, anti-RBD-specific ratio:0.7) P< 0.001).


      Early 3rd trimester as compared to second trimester and late 3rd trimester maternal SARS-CoV-2 immunization enhances transplacental antibody transfer and increased neonatal antibody levels. Our findings highlight that vaccination of pregnant women early in the third trimester may optimize neonatal seroprotection.