ABSTRACT
Objective: To explore maternal humoral immune responses to severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) infection and the rate of vertical transmission. Study Design: A prospective cohort study was conducted at two university-affiliated medical centers. Women positive for SARS-CoV-2, as determined by reverse-transcription-polymerase-chain-reaction (RT-PCR), during pregnancy were enrolled just prior to delivery. Levels of anti-SARS-CoV-2 nucleocapsid IgG, spike IgG and spike-IgM were tested in maternal and cord blood at delivery, and neonatal nasopharyngeal swabs were subjected to PCR testing. The primary endpoint was the rate of vertical transmission, defined as either positive neonatal IgM, positive neonatal IgG with sero-negative mother or positive neonatal PCR. The rate of vertical transmission was estimated to be 7% when defined by RT-PCR. Assuming that using serology tests increases the rate to 10% versus 0% in non-infected population, 71 women were required (80% power, 5% one-sided alpha) Results: Among 72 women, 36 (50%), 39 (54%) and 30 (42%) were positive for anti-spike-IgM, anti-spike-IgG and anti-nucleocapsid-IgG, respectively (p < 0.0001 for IgG antibodies;table). At least 8/72 (11%) neonates were infected in utero;one had a positive PCR and seven had positive IgG while their mothers were seronegative for the same IgG. IgM was not detected in cord blood. Anti-nucleocapsid-IgG and anti-spike-IgG were detected in 83% and 85% of neonates of seropositive mothers, respectively (Pearson coefficient correlation 0.8, p< 0.001). The highest rate of positive maternal serology tests was 8-12 weeks post-infection (89% anti-spike IgG, 78% anti-spike IgM and 67% anti-nucleocapsid IgG). Thereafter, the rate of positive serology tests declined gradually;at 20 weeks post-infection, only anti-spike IgG was detected in 33-50% (figure). Conclusion: The rate of vertical transmission was at least 11%. Vaccination should be considered 3 months post-infection in pregnant women due to a decline in antibody levels. [Formula presented] [Formula presented]