Maternal Antibody Response, Neutralizing Potency, and Placen
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The study characterizes maternal immune response after severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection during pregnancy and quantifies the efficiency of transplacental antibody transfer.

Researchers conducted a prospective cohort study of pregnant patients who tested positive for SARS CoV-2 infection at any point in pregnancy and collected paired maternal and cord blood samples at the time of delivery. An ELISA and neutralization assays were performed to measure maternal plasma and cord blood concentrations and neutralizing the potency of IgG, IgA, and IgM antibodies directed against the SARS-CoV-2 spike protein.

Differences in concentrations according to symptomatic compared with asymptomatic infection and time from a positive PCR test result to delivery were analyzed using nonparametric tests of significance. The ratio of cord to maternal anti–receptor-binding domain IgG titers were analyzed to assess transplacental transfer efficiency.

Thirty-two paired samples were analyzed.

- Detectable anti–receptor-binding domain IgG was detected in 100% of maternal and 91% of cord blood samples.

- Functional neutralizing antibody was present in 94% of the maternal and 25%of cord blood samples.

- Symptomatic infection was associated with a significant difference in median maternal anti–receptor-binding domain IgG titers compared with asymptomatic infection.

- Median maternal anti–receptor-binding domain IgG titers were not significantly higher in patients who delivered more than 14 days after a positive PCR test result compared with those who delivered within 14 days. The median cord/maternal antibody ratio was 0.81.

These results demonstrate robust maternal neutralizing and anti–receptor-binding domain IgG response after SARS-CoV-2 infection, yet a lower-than-expected efficiency of transplacental antibody transfer and a significant reduction in neutralization between maternal blood and cord blood.