Longitudinal analysis of passively and actively acquired SARS-CoV-2 antibodies in infants with repeat newborn screening samples.

Large-scale studies that investigate longitudinal changes in SARS-CoV-2 antibody reactivity in newborn infants are limited. Infants acquire maternal IgG antibodies that decay after birth; if infected, they produce infant-derived IgG, IgA, and IgM antibodies. The New York State Newborn Screening Program (NYS NSP) collects dried blood spots (DBS) from infants at birth and follow-up specimens from a select group of infants, many of whom are premature. We tested 100,318 remnant DBS from 50,036 infants with repeat specimens received between November 2019 and November 2021 for SARS-CoV-2 IgG antibodies; 9611 infants were IgG reactive at birth and 630 seroconverted for SARS-CoV-2 IgG. The first infant seroconversion occurred in March 2020. Infants antibody-reactive at birth were less likely to have low or very low birthweight or be from a multiple birth; infants with repeat specimens were less likely to be reactive at birth than those with single specimens. Antibody decay occurred in a non-linear process with initial rapid decay followed by slower decay (half-life of 22-23 days for 0-30 days after birth, 37-38 days for > 30 days after birth). Seroconversion was confirmed by retesting IgG seroconverting infants for detectable IgA and IgM SARS-CoV-2 antibodies.