Neonatal SARS-CoV-2 immunoglobulin G antibodies at delivery and their impact on COVID-19.

OBJECTIVE: To assess neonatal SARS-CoV-2 anti-spike IgG antibody levels after maternal mRNA COVID-19 vaccination and/or infection during pregnancy and evaluate their protective effect.

METHODS: Prospective observational study, conducted from January 2021 to December 2022. Infants were tested for anti-spike IgG antibodies at birth and then every 3 months until disappearance of titer. A follow-up was done for SARS-CoV-2 infection up to 12 months.

RESULTS: In total, 147 newborns were enrolled with a median (IQR) gestational age of 39.60 weeks (38.3-40.4). Median (IQR) titers in UA/ml at 2 days were higher (P < .001) in newborns of vaccinated 7063.7 (2841.4-14,448.1), than of infected mothers 372.7 (158.00-884.90). Titers dropped significantly during the follow-up but 50% still had a detectable titer at 6 months. A high antibody titer at 2 days led to a longer persistence (HR 0.89, IC 95% 0.83-0.96, P = .004). In total, 36 infants were infected during the first months of life coinciding with the Omicron variant. Fifty percent had detectable antibodies during the infection period. Relationship between high IgG titers and month of infection was inverse (RHO - 0.52, P = .009).

CONCLUSION: Though a high antibody titer at birth led to longer persistence, no protective effect against infection was found. As newborns are a high risk group for COVID-19, avoiding transmission during the first year of life is important.