LONGITUDINAL SARS-CoV-2 ANTIBODY RESPONSE in PREGNANCY and TRANSPLACENTAL TRANSFER

ABSTRACT

Background: Longitudinal assessment of SARS-CoV-2 antibody (Ab) response during pregnancy after infection and transplacental transfer may inform durability of maternally derived Ab for mothers and infants. Methods: Between October 2020-September 2021, pregnant people testing SARS-CoV-2 IgG positive by Abbott Architect chemiluminescent immunoassay (CMIA) for anti-nucleocapsid (N) antibody (semi-quantitative index ≥1.4 considered IgG+) during pregnancy or delivery in a seroprevalence study, or identified with RT-PCR+ results via medical records, were invited to enroll in a longitudinal evaluation of maternal Ab responses and transplacental transfer. Maternal blood collected at 1, 2, 3, and 6 months after enrollment and maternal and cord blood collected at delivery were tested with the same assay. Results: Among 40 participants testing IgG+ for anti-N, 31 (78%) had a prior RT-PCR+ result. Median age was 32 years (IQR 29-35);27 (68%) enrolled during pregnancy at median 18 weeks gestation (IQR 13-33), while 13 (33%) enrolled at delivery or early postpartum. Median Abbott index was 3.06 (IQR 1.96-5.74) at first IgG+ result obtained at a median of 9 weeks (IQR 4-16) after RT-PCR+ result, for those with a known RT-PCR. Among 23 participants with ≥2 samples, 50% had IgG results below positivity threshold at median 17 weeks (IQR 12-28) after first IgG+ result (Figure). Seventeen mother-infant pairs had delivery samples collected at median 66 days (IQR 60-71 days) from maternal RT-PCR+ result. Six (35%) maternal samples remained IgG+ (median Abbott index 2.97 [IQR 2.35-7.01]) at delivery (gestational age 30-40 weeks) with all 6 paired cord sera testing IgG+ (median Abbott index 4.30 [IQR 2.93-7.22]). Median placental transfer ratio of maternally derived IgG Abs based on a positive Abbott index was 1.13 (95%CI 0.98-1.30) among mothers with samples remaining IgG+ at delivery. Conclusion: Within 4 months after first IgG+ result primarily in second trimester, about half of pregnant persons had SARS-CoV-2 IgG anti-N Ab levels below the Abbott CMIA positive threshold. Among evaluable mother-infant pairs, two-thirds of mothers no longer tested anti-N IgG+ at delivery. Transplacental transfer of maternal antibodies was confirmed in all infants born to mothers with samples remaining IgG+ at delivery. Durability of maternal SARS-CoV-2 Ab response and transplacental transfer following infection has implications for maternal and neonatal susceptibility to SARS-CoV-2 infection.