Third trimester messenger RNA COVID-19 booster vaccination upsurge maternal and neonatal SARS-CoV-2 immunoglobulin G antibody levels at birth.

Objective: BNT162b2 messenger RNA (mRNA) COVID-19 vaccine administered during pregnancy was found to produce a strong maternal immunoglobulin (IgG) response which crosses the placenta to the newborn. Our aim was to evaluate maternal and neonatal SARS-CoV-2 IgG antibody levels at birth, following a COVID-19 booster vaccine during the third trimester.

Study Design: A prospective cohort study including women admitted to delivery ward at least 7 days after their BNT162b2 (Pfizer/BioNTech) booster vaccination without a prior clinical COVID-19 infection. SARS-CoV-2 IgG antibodies levels were measured in maternal blood upon admission to delivery and in the umbilical blood within 30 min following delivery. The correlation between antibody titers, feto-maternal characteristics, maternal side effects following vaccination, and time interval from vaccination to delivery were analyzed.

Results: Between September to November 2021, high antibody levels were measured in all 102 women and 93 neonatal blood samples, at a mean ± standard deviation duration of 7.0 ± 2.9 weeks after the third vaccine. We found positive correlation between maternal and neonatal antibodies (r = 0.73, 95% confidence interval [CI] 0.61 to 0.81, p < 0.001), with neonatal titers approximately 1.4 times higher compared to maternal titers. In the multivariable analysis maternal antibody levels dropped by -7.2% (95% CI -12.0 to -2.3%, p = 0.005) for each week that passed since the receipt of the third vaccine dose. In contrary, systemic side effects after the third vaccine were associated with higher maternal antibody levels of 52.0% (95% CI 4.7 to 120.8%, p = 0.028). Also, for each 1 unit increase in maternal body mass index, maternal antibody levels increased by 3.6% (95% CI 0.4 to 6.9%, p = 0.025).

Conclusions: BNT162b2 mRNA COVID-19 booster dose during the third trimester of pregnancy was associated with strong maternal and neonatal responses as reflected by maternal and neonatal SARS-CoV-2 IgG antibody levels measured at birth. These findings support the administration of the COVID-19 booster to pregnant women to restore maternal and neonatal protection during the ongoing pandemic.