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Mechanisms for protecting neonates against infection begin in utero. To assess maternal transfer of anti–SARS-CoV-2 IgG antibodies to the fetus, researchers tested maternal and umbilical cord sera for IgG and IgM antibodies to the SARS-CoV-2 spike protein receptor-binding domain in a racially and ethnically diverse cohort delivering at an academic medical center in Philadelphia.
Among 1471 matched maternal-umbilical samples, those from 83 mothers and 72 infants were positive for anti–spike protein IgG antibodies. Among the seropositive mothers, 60% were considered to have had an asymptomatic infection, suggesting maternal-to-fetal transfer of IgG anti–spike protein antibodies after both asymptomatic and symptomatic COVID-19. The mean transfer ratio of anti–spike protein IgG antibodies was 0.9 and increased with time between maternal infection and delivery. Anti–spike protein IgM antibodies were not detected in umbilical sera.
Flannery DD et al. Assessment of maternal and neonatal cord blood SARS-CoV-2 antibodies and placental transfer ratios. JAMA Pediatr 2021 Jan 29; [e-pub]. (https://doi.org/10.1001/jamapediatrics.2021.0038)
Comment
These findings are reassuring in showing that pregnant women infected with SARS-CoV-2 can efficiently transfer anti–spike protein IgG antibodies to their fetuses, thereby helping to protect their newborns from infection (in addition, immune mothers who breast-feed continue to transfer protective antibodies to their infants). It's also reassuring that no umbilical sera samples contained anti–spike protein IgM antibodies, suggesting that intrauterine SARS-CoV-2 infection did not occur. Pregnant women who become eligible for COVID-19 vaccination must decide whether to receive the vaccine based on still-limited safety data (CDC COVID-19 vaccines page). The observation that anti–spike protein IgG antibodies can pass from mother to fetus may be an important factor for pregnant women when deciding about receiving the vaccine.