Infant Antibodies After Maternal COVID-19 Vaccination During Pregnancy or Postpartum

We describe the kinetics of maternally derived antibodies in infants in the first 6 months of life following 2- or 3-dose maternal vaccination during pregnancy or postpartum.

This prospective, multicenter cohort study enrolled infants born to mothers vaccinated with 2- (n = 280) or 3-dose (boosted) monovalent messenger RNA vaccines in pregnancy (n = 202) or to mothers vaccinated postpartum (n = 36) from July 2021 to January 2022. Binding (immunoglobulin G to S and receptor-binding domain), pseudovirus, and live neutralizing antibody (nAb) geometric mean titers (GMTs) to vaccine and Omicron BA.1/BA.5 strains were measured at birth and 2 and 6 months of age. Antibody half-life and the effect of maternal or infant COVID-19 infection were assessed.

Significantly higher GMTs of binding antibody and nAb to all antigens were present at birth and 2 months in infants of boosted mothers (P < .01) and higher titers to the vaccine strain, but not Omicron BA.1 and BA.5, persisted up to 6 months of age in infants of boosted mothers compared with the other groups (P < .01). Higher infant antibody titers at delivery and 6 months of age were associated with a booster dose during pregnancy and maternal prenatal and infant COVID-19 infection. Maternal infection status or vaccine regimen did not influence the half-life of infant antibodies.

A maternal COVID-19 booster in pregnancy results in significantly higher functional antibody titers in infants compared with 2 doses in pregnancy or postpartum. High titers at birth and maternal hybrid immunity result in persistently elevated titers in infants for 6 months.