Maternal-Infant Respiratory Syncytial Virus and Influenza A Virus Antibody Transfer in Preterm and Full-term Infants

Background. Immunization against influenza and respiratory syncytial virus (RSV) protects pregnant individuals and their infants against infection via transplacental transport of immunoglobulin G (IgG). We sought to evaluate the quantity and efficiency of maternal influenza- and RSV-specific IgG transfer in pregnancies with preterm and full-term deliveries. Methods. Delivery samples from 115 maternal-infant pairs (2018-2021) were analyzed for RSV prefusion F and IAV-H3 and IAV-H1 antibodies using electrochemiluminescence assays. We used Wilcoxon rank sum tests, t tests, Pearson correlation coefficients (PCCs), and linear regression to evaluate distributions of IgG results by maternal influenza vaccination status and preterm birth (<37 weeks). Results. Approximately 70% of pregnant persons received influenza vaccine. Maternal and cord antibody concentrations were highest in the influenza-vaccinated group for IAV-H3 and IAV-H1 regardless of preterm birth status (maternal H3, P = .004; cord H3, P = .03; maternal H1, P = .0001; cord H1, P = .0002). Preterm infants had significantly lower cord to maternal IgG transfer ratios for IAV-H3 and RSV when compared with full-term infants (P ≤ .05). Correlations between maternal and cord IgG concentrations were significant (P ≤ .001) for all 3 viruses, with the strongest correlation for H3 (PCC: IAV-H3, 0.77; IAV-H1, 0.68; RSV, 0.62). Associations between maternal IgG transfer and preterm birth were significant for IAV-H3 and RSV (IAV-H3, β = −0.42; RSV, β = −0.63; P ≤ .05). Conclusions. Maternal antibody following vaccination or infection is readily transferred across the placenta. Preterm infants have higher influenza IgG following maternal influenza vaccination and are at highest risk of lower IgG transfer ratios without vaccination.