PC1052: Screening for sars-cov-2 Antibodies in Cord Blood to Identify Neonates with In-utero sars-cov-2 Infections

Background: Although screening for SARS-CoV-2 infection is performed at delivery, there are limited data on rates of mother-to-child transmission (MTCT), as screening is not typically done in earlier stages of pregnancy. Thus, rates of MTCT with undiagnosed, asymptomatic, or symptomatic infections during pregnancy are unknown and are likely greater than current estimates of 2-8%.

Methods: Cord bloods were collected at LAC+USC Medical Center from October 2021 to April 2022 and evaluated for SARS-CoV-2 specific IgG using the Luminex™ xMAP® SARS-CoV-2 Multi-Antigen Antibody EUA Assay that detects antibodies to SARS-CoV-2 antigens N, RBD and S1. A positive IgG result was defined as IgG MFI >700. Mean Fluorescence Intensity (MFI) can differentiate between natural infection (positive for both N and RBD or S1) and vaccine response or past infection (positive for RBD or S1 only). Results were analyzed using the Luminex™ xPonent EUA software using the MPMultiCoV2 protocol. A subset of positive samples were assessed for IgM and IgA antibodies (N, S1, RBD) using a modified version of the Luminex™ assay. Pre-COVID-19 cord blood samples were used to define threshold. A positive IgM result was defined as IgM MFI >24. A positive IgA result was defined as IgA MFI >102.

Results: Over 500 samples have been collected to date. Among 384 samples analyzed, 328 (85.4%) were anti-RBD IgG positive (RBD MFI >700) indicating immunity to SARS-CoV-2 due to either previous infection or vaccination of the mother (Figure 1). 199 of these 328 (60.7%) were anti-RBD IgG positive and anti-N IgG negative indicating immunity due to vaccination or past infection in which N has waned (Figure 1). Importantly, 129 of these 328 (39.3%) were anti-RBD IgG positive and also anti-N IgG positive indicating past maternal infection (Figure 1). These 129 were assessed for IgM and IgA antibodies. 16 out of 129 had high levels of anti-RBD IgA (RBD MFI >102) and/or IgM (RBD MFI >24) above threshold indicative of an in-utero transmission, giving a MTCT rate of 12.4% (Figure 2).

Conclusion: Among 384 cord blood samples, 85.4% had anti-RBD antibodies indicative of past maternal infection and/or vaccination and 39.3% had past infection. IgM and/or IgA antibodies were present in 16 of 129 (12.4%) samples with maternal past infection indicating possible in-utero infection and/or transmission. Cord blood screening is a potential tool to identify SARS-CoV-2 infected and/or exposed neonates who should then be followed for long-term consequences of MTCT of SARS-CoV-2.