Timing of SARS-CoV-2 vaccination during the third trimester of pregnancy and transplacental antibody transfer: a prospective cohort study

Objective: We aimed to assess the impact of early versus late third-trimester maternal severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) vaccination on transplacental transfer and neonatal levels of SARS-CoV-2 antibodies. Methods: Maternal and cord blood sera were collected following term delivery after antenatal SARS-CoV-2 BNT162b2 mRNA vaccination, with the first vaccine dose administered between 27 and 36 weeks of gestation. 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. Results: The study cohort consisted of 171 parturients-median age 31 years (interquartile range (IQR) 27 - 35 years); median gestational age 39(+5) weeks (IQR 38(+5)-40(+4) weeks)-83 (48.5%) were immunized in early thrird-trimester (first dose at 27-31 weeks) and 88 (51.5%) were immunized in late third trimester (first 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 versus late third trimester vaccination (median 9620 AU/mL (IQR 5131-15332 AU/mL) versus 6697 AU/mL (IQR 3157 - 14731 AU/mL), p 0.02), and were positively correlated with increasing time since vaccination (r = 0.26; p 0.001). Median antibody placental transfer ratios were increased following early versus late third-trimester immunization (anti-S ratio: 1.3 (IQR 1.1-1.6) versus 0.9 (IQR 0.6-1.1); anti-RBD-specific ratio: 2.3 (IQR 1.7-3.0) versus 0.7 (IQR 0.5-1.2), p < 0.001). Neutralizing antibodies placental transfer ratio was greater following early versus late third-trimester immunization (median 1.9 (IQR 1.7-2.5) versus 0.8 (IQR 0.5-1.1), p < 0.001), and was positively associated with longer duration from vaccination (r = 0.77; p < 0.001). Conclusions: Early compared with late third-trimester maternal SARS-CoV-2 immunization enhanced transplacental antibody transfer and increased neonatal neutralizing antibody levels. Our findings highlight that vaccination of pregnant women early in the third trimester may enhance neonatal sero-protection. (C) 2021 European Society of Clinical Microbiology and Infectious Diseases. Published by Elsevier Ltd. All rights reserved.

Automated summary

This study aimed to evaluate the impact of maternal vaccination against SARS-CoV-2 in early versus late third trimester on transplacental transfer and neonatal levels of antibodies. The results showed that early vaccination in pregnancy enhanced transplacental antibody transfer and increased neonatal neutralizing antibody levels, indicating that early vaccination in the third trimester may enhance neonatal immune protection.