Clinical assessment of transplacental transfer of maternal SARS-CoV-2 IgG antibodies against spike and nucleocapsid proteins: A chemiluminescence microparticle immunoassay study

Understanding the safety and efficacy of COVID-19 vaccines in pregnant women and their neonates is crucial for understanding maternal and fetal outcomes, particularly the extent of passive immunity against SARS-CoV-2 which can be imparted to the neonates. The purpose of this study was to evaluate the transplacental transfer of maternal SARS-CoV-2 IgG antibodies against the spike (S) and nucleocapsid (N) proteins to neonates and understand whether factors like maternal comorbidities, gestational weeks, and neonatal birth weight have an influence on placental transfer ratios (PTR). A total of 57 pregnant women were assessed for SARS-CoV-2-specific IgG antibodies at delivery, and corresponding antibody titers were also measured in their neonates immediately after delivery. The PTRs for anti-S and anti-N IgG were calculated, and statistical analyses were performed for identifying potential influencing factors. The mean PTR for anti-S IgG was 1.38, suggesting effective placental transfer, whereas anti-N IgG had a lower PTR of 1.13, indicating limited transfer. A strong positive correlation was observed between maternal and neonatal anti-S IgG (r = 0.558, p < 0.01), whereas maternal and neonatal anti-N IgG correlated weakly (r = 0.402, p = 0.02). No significant associations were found between PTRs and maternal age, gestational weeks, neonatal birth weight, or comorbidities. Our study inferred the efficient transfer of maternal anti-S IgG, potentially conferring early neonatal immunity against SARS-CoV-2. However, the long-term persistence of these neonatal antibodies are questionable and remains an important research prospect. This study underscored the critical role of maternal vaccination for neonatal protection and can help form evidence based rational vaccination strategies for maximum neonatal protection.