Transplacental Respiratory Syncytial Virus and Influenza Virus Antibody Transfer in Alaska Native and Seattle Mother-Infant Pairs.

Background: Alaska Native (AN) infants are at risk for severe disease due to respiratory syncytial virus (RSV) and influenza. Maternal immunization protects young infants through transplacental antibody transfer. RSV- and influenza-specific transplacental antibody transfer in mother-infant pairs has not previously been evaluated in the AN population.

Methods: Serum samples collected during pregnancy and at birth from AN mother-infant pairs in the Yukon-Kuskokwim Delta region (YKD) of Alaska (2000-2011; n = 75) and predominantly white pairs in Seattle, Washington (2014-2016; n = 57), were tested for RSV and influenza antibody using a microneutralization and hemagglutination inhibition assay, respectively, and compared between sites.

Results: Mean RSV antibody concentrations in pregnant women in YKD and Seattle were similar (log2 RSV antibody 10.6 vs 10.7, P = .86), but cord blood RSV antibody concentrations were significantly lower in infants born to mothers in YKD compared with Seattle (log2 RSV antibody 11.0 vs 12.2, P < .001). Maternal and cord blood influenza antibody concentrations were lower for women and infants in YKD compared with Seattle for all 4 influenza antigens tested (all P < .05). The mean cord to maternal RSV antibody transfer ratio was 1.15 (standard deviation [SD], 0.13) in mother-infant pairs in Seattle compared with 1.04 (SD, 0.08) in YKD. Mean cord blood to maternal antibody transfer ratios for influenza antigens ranged from 1.22 to 1.42 in Seattle and from 1.05 to 1.59 in YKD.

Conclusions: Though the transplacental antibody transfer ratio was high (>1.0) for both groups, transfer ratios for RSV antibody were significantly lower in AN mother-infant pairs. Further studies are needed to elucidate the impact of lower transplacental antibody transfer on infant disease risk in rural Alaska.Alaska Native and continental US mother-infant pairs have high transplacental antibody transfer ratios (>1.0) for influenza and respiratory syncytial virus, but anti-respiratory syncytial virus antibody levels are significantly lower in Alaska Native pairs than in those from the continental US.