Maternal immunoglobulin (Ig)G antibodies to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) were transferred across the placenta after asymptomatic as well as symptomatic infection during pregnancy, according to a study published in JAMA Pediatrics. The study also found that cord blood antibody concentrations correlated with maternal antibody concentrations and with duration between onset of infection and delivery.
“Maternally derived antibodies are a key element of neonatal immunity. Understanding the dynamics of maternal antibody responses to SARS-CoV-2 infection during pregnancy and subsequent transplacental antibody transfer can inform neonatal management as well as maternal vaccination strategies,” wrote Dustin D Flannery, Children’s Hospital of Philadelphia, Philadelphia, Pennsylvania, and colleagues. “Our findings demonstrate the potential for maternally derived SARS-CoV-2-specific antibodies to provide neonatal protection from coronavirus disease 2019 (COVID-19).”
Among 1,471 mother/newborn dyads for which matched sera were available, SARS-CoV-2 IgG and/or IgM antibodies were detected in 83 of 1,471 women (6%; 95% confidence interval [CI], 5%-7%) at the time of delivery. Most (60%) women who were seropositive were asymptomatic for COVID-19.
Of 83 infants born to seropositive women, IgG was detected in cord blood from 72 infants (87%; 95% CI, 78%-93%), while IgM antibodies were not detectable in any of these 72 seropositive infants. Among the 11 seropositive women with infants who were seronegative, 5 women were seropositive only by IgM, and the remaining 6 women had significantly lower geometric mean IgG concentrations compared with the 72 women with seropositive infants (1.27 vs 5.22 arbitrary units/mL; P = 0.005).
Further, the researchers found that cord blood IgG concentrations were positively correlated with maternal IgG concentrations (r = 0.886; P < 0.001). They also observed efficient transfer of IgG antibodies from women who were seropositive with transfer ratios ≥1.0 in 40 of the 72 infants who were seropositive. Placental transfer ratios were not different among infants born to mothers with asymptomatic or symptomatic illness. Transfer ratios, on the other hand, increased with increasing time between onset of maternal infection and delivery (r = 0.620; P < 0.001).
“When vaccines are widely available, the optimal timing of maternal vaccination during pregnancy will need to consider maternal and fetal factors including the time needed to ensure neonatal protection,” the authors noted. “Further studies are needed to determine if SARS-CoV-2 antibodies are protective against newborn infection; if so, at what concentration; and whether the transplacental kinetics of vaccine-elicited antibodies are similar to naturally acquired antibodies.”