Association of SARS-CoV-2 Serology in Cord Blood with Maternal COVID-19 Vaccination Status: A Prospective Cohort Study

Introduction: Maternal vaccination against Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) offers an opportunity to protect both pregnant women and their newborns. Understanding how vaccine timing and dosing influence transplacental antibody transfer is essential for optimising perinatal immunisation strategies. Aim: To assess the SARS-CoV-2 Immunoglobulin G (IgG) status and its association with maternal Coronavirus Disease 2019 (COVID-19) vaccination status. Materials and Methods: A prospective observational cohort study was conducted at the Department of Neonatology, Paediatrics, Swami Rama Himalayan University, Dehradun, Uttarakhand, India, from October 2021 to January 2022. The study included all 200 mothers who delivered during the study period and their neonates. Maternal SARS-CoV-2 infection and vaccination status were recorded on admission. Umbilical cord blood was collected at birth and IgG was assessed. Neonates born to mothers with confirmed infection underwent polymerase chain reaction testing. Primary analysis compared Cord blood IgG concentrations across vaccination subgroups and examined associations with the number of doses, interval since vaccination, and gestational age at delivery. The Kruskal-Wallis test was used to determine statistically significant differences between groups. A two-tailed p-value<0.05 was considered statistically significant. Results: The mothers had a mean age of 27.1±4.3 years (median 26 years; range 18-45years) with a mean gestational age at delivery of 37.64±2.39 weeks (median 38 weeks; range 26-41weeks), and neonatal birth weight was 2.72±0.60 kg. Cord blood IgG concentrations were markedly higher in neonates of vaccinated mothers than in those of unvaccinated mothers (p-value=0.001). Titers did not differ between one-dose and two-dose recipients. Antibody concentrations declined as the interval between the final vaccine dose and delivery lengthened, within nine months of vaccination (76.72±10.64 AU/mL; n=52), at 9-12 months (10.65±7.73 AU/mL; n=10), and at 12-14 months (6.92±6.07 AU/mL; n=8; p-value=0.016), while later gestational age at birth was associated with higher titers. Conclusion: Maternal SARS-CoV-2 vaccination, particularly when administered close to delivery, enhances passive antibody transfer to the newborn, whereas immunity acquired through infection alone is less effective. These findings support the use of universal vaccination during pregnancy and suggest that a booster dose in late pregnancy may maximise neonatal protection.