The Effect of Gestational Age at BNT162b2 mRNA Vaccination on Maternal and Neonatal Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) Antibody Levels

Background Coronavirus disease 2019 (COVID-19) during pregnancy and early infancy can result in severe disease. Evaluating the effect of gestational age at the time of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) vaccination on maternal antibody levels and transplacental antibody transfer has important implications for maternal care and vaccination strategies. Methods Maternal and cord blood sera were collected from mother-newborn dyads (n = 402), following term delivery after antenatal 2-dose SARS-CoV-2 BNT162b2 mRNA vaccination. SARS-CoV-2 spike protein (S) and receptor binding domain (RBD)-specific IgG levels were evaluated in the samples collected. Results Median anti-S and anti-RBD-specific IgG levels in maternal sera at the time of delivery were lowest following first-trimester vaccination (n = 90; anti-S IgG: 76 AU/mL; anti-RBD-specific IgG: 478 AU/mL), intermediate in those vaccinated in the second trimester (n = 124; anti-S IgG: 126 AU/mL; anti-RBD-specific IgG: 1263 AU/mL), and highest after third-trimester vaccination (n = 188; anti-S IgG: 240 AU/mL; anti-RBD-specific IgG: 5855 AU/mL). Antibody levels in neonatal sera followed a similar pattern and were lowest following antenatal vaccination in the first trimester (anti-S IgG: 126 AU/mL; anti-RBD-specific IgG: 1140 AU/mL). In a subgroup of parturients vaccinated in the first trimester (n = 30), a third booster dose was associated with significantly higher maternal and neonatal antibody levels. Conclusions These results suggest a considerable antibody waning throughout pregnancy in those vaccinated at early gestation. The observed boosting effect of a third vaccine dose hints at its potential benefit in those who completed the 2-dose vaccine series at early pregnancy or before conception. The impact of antenatal immunization timing on SARS-CoV-2 transplacental antibody transfer may influence neonatal seroprotection. Lower antibody titers were found after maternal vaccination at early pregnancy, suggesting considerable antibody waning throughout gestation, with a potential role of a third vaccine dose. The effect of immunization timing on the transplacental antibody transfer may influence neonatal seroprotection.

Automated summary

Maternal antibody levels and transplacental antibody transfer vary based on the gestational age at the time of SARS-CoV-2 vaccination, with lowest levels observed in those vaccinated in the first trimester. A third booster dose may enhance antibody levels and could be beneficial for those who completed the 2-dose vaccine series early in pregnancy.