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Protection from infection through transfer of IgG antibodies via cord blood after maternal SARS-CoV-2 infection during pregnancy

Author Prof. E. Harms, University Department of Pediatrics Münster

Newborns are protected from infection by their innate, immature immune system and by diaplacentally transferred maternal antibodies (Abs). A research team from Philadelphia (USA) looked at a large number of SARS-CoV-2 infection cases that occurred during pregnancy and studied the antibodies to the receptor-binding domain of the SARS-CoV-2 spike protein found in the maternal sera and the neonatal cord blood [1]. The study looked at the sera of 1471 mother/newborn dyads. IgG Abs to SARS-CoV-2 were detected in 83 mothers but only in 72 newborns. However, IgM Abs were not detected in any of the newborns. IgM Abs were detected in 48 mothers with higher titres in those with symptomatic infections.
50 of the 83 mothers were asymptomatic and did not know they were infected. The IgG Ab titre concentration did not correlate with disease progression except in severe cases. Transfer ratios (titre in mother/child) increased with an increase of time between the onset of maternal infection and delivery but were not associated with severity of maternal infection. The transfer ratio in 40 of the 72 seropositive newborns was ≥ 1.

Comment: This study contains several important pieces of information:
The majority of mothers found to have Abs had not even noticed the infection. This is a general problem of the COVID-19 pandemic, which makes it almost impossible to contain infections.
None of the 83 newborns showed IgM Abs, meaning that there were no cases of intrauterine infection. The few described cases of vertical transmission of SARS-CoV-2 infection to the foetus are exceptions.
The IgG Abs transferred are likely to protect the newborns against infection, although it’s not yet clear how long this protection lasts and how effective it is. SARS-CoV-2 vaccination in pregnancy could provide the newborn with temporary protection against infection.

[1] Flannery DD, Gouma S, Dhudasia MB et al. (2021) Assessment of Maternal and Neonatal Cord Blood SARS-CoV-2 Antibodies and Placental Transfer Ratios. JAMA Pediatr.doi:10.1001/jamapediatrics.2021.0038.