Infants whose mothers received a COVID-19 booster during pregnancy had higher antibody levels through 6 months of age compared with those whose mothers received only 2 doses or were vaccinated postpartum, according to a US cohort study of 518 infants.

The study, conducted between July 6, 2021, to January 31, 2022, at 9 academic centers, compared 3 groups: 280 infants whose mothers received 2 doses of an mRNA vaccine during pregnancy, 202 infants whose mothers received a third (booster) dose during pregnancy, and 36 infants whose mothers were vaccinated only postpartum.

Researchers measured infant serum immunoglobulin G (IgG) binding antibodies and neutralizing antibodies (nAbs) to the SARS-CoV-2 spike protein and Omicron variants BA.1 and BA.5 at birth, 2 months, and 6 months.

At birth and 2 months, infants of mothers who received a booster had significantly higher geometric mean titers (GMTs) of both binding and neutralizing antibodies. At 6 months, higher D614G antibody levels persisted in the booster group, although neutralization against Omicron BA.1 and BA.5 was not significantly different among the groups.

All infants in the booster group had detectable binding antibodies to the spike protein and receptor-binding domain at 6 months. Detection rates were lower in the other groups. Transplacental antibody transfer was more efficient in the booster group. The mean transfer ratio for Omicron BA.5 nAbs was 1.76 in the booster group and 1.13 in the two-dose group.

The estimated half-life of anti-spike IgG in infants was 36.4 days; for anti-RBD IgG, it was 35.3 days. The half-life for pseudovirus nAbs was shorter at 28.2 days.

Maternal COVID-19 infection during pregnancy was also associated with higher infant antibody levels. When combined with vaccination—referred to as hybrid immunity—maternal infection further increased antibody persistence.

By 6 months, 32% in the booster group, 26% in the two-dose group, and 25% in the postpartum group had confirmed SARS-CoV-2 infection. No hospitalizations or deaths occurred in the infant cohort during follow-up.

Breastfeeding was not associated with higher infant antibody levels.

Full Disclosures can be found in the published study.

Source: Pediatrics