The goal of this study was to investigate the relationship between anti-SARS-CoV-2-Spike
IgG titers passively transferred to the fetus from maternal vaccination during pregnancy and timing of infant
SARS-CoV-2 infection. Pregnant, vaccinated individuals (n = 105) and their infants (n = 107) were enrolled in a prospective cohort study from July 2021 to June 2022, linking infant anti-Spike
IgG titer at birth to risk of
SARS-CoV-2 infection in the first fifteen months of life. Cord blood sera were collected at delivery and infant sera were collected at two and six months of age. Anti-SARS-CoV-2-Spike
IgG levels were quantified in cord and infant sera using an
enzyme-linked
immunosorbent assay. Infants were followed for
SARS-CoV-2 infection through fifteen months of age. Anti-SARS-CoV-2-Spike
IgG titers in infants declined significantly with increased age (p < 0.001). Infants with higher anti-Spike cord blood levels had significantly longer disease-free intervals prior to
infection with SARS-CoV-2 (p = 0.027). While higher anti-Spike
IgG titer at two months of age was associated with a longer interval to
infection through nine months of age (p = 0.073), infant anti-Spike
IgG titers by six months of age had no impact on disease-free interval. This cohort study suggests that passively transferred maternal
IgG is protective against infant
SARS-CoV-2 infection, with higher antibody levels at birth significantly associated with longer disease-free intervals. Infant
antibodies and protection from
SARS-CoV-2 infection wane significantly after six months, suggesting that vaccination is needed at this stage to optimize protection against
COVID-19.