O2111: Boosting the Maternal Antibody Response Against sars-cov-2 Results in Increased Transfer to Infants During Pregnancy

Background: Passive transfer of IgG antibodies through the placenta during pregnancy, primarily third trimester, reduces the incidence of various infectious diseases in infants. Increased maternal antibody levels to influenza, respiratory syncytial virus, pertussis and rubella as well as implementation of third trimester influenza and pertussis vaccination strategies correlate with improved infant protection against these infections. The development of protective immunity against SARS-CoV-2 and the response to novel messenger RNA vaccines in pregnant women is currently poorly understood and limits the ability to determine whether passive immunity during pregnancy can protect infants. Our objective is to evaluate the passive transfer of antibodies during pregnancy after SARS-CoV-2 infection or maternal immunization.

Methods: Prospective multi-center cohort study of pregnant women ≥18 years of age who acquired SARS-CoV-2 infection and/or received at least one dose of mRNA SARS-CoV-2 vaccine before or during pregnancy. Maternal infection confirmation was determined by SARS-CoV-2 PCR and further evaluated using sera immunoglobulin (IgG) against the SARS-CoV-2 nucleoprotein, which is not found in infection naïve immunized patients. Sera IgG against the spike protein of SARS-CoV-2 from maternal venous serum and cord blood were quantitatively measured using a multiplex serology strategy and compared by vaccination status using exact Wilcoxon rank sum tests.

Results: Of the eight couplets with available cord blood, each mother was infected with SARS-CoV-2 prior to delivery with confirmatory nucleoprotein concentrations in both maternal and fetal circulation. Three of these mothers were vaccinated prior to delivery. Quantitative measurement and vaccination status are summarized (Figure 1 and 2). SARS-CoV-2 antibody concentrations, as measured by anti-spike IgG as a median fluorescence intensity MFI, were higher for mothers with hybrid immunity who were infected and vaccinated prior to delivery, in both maternal (p = 0.04) and fetal circulation (p = 0.04).

Conclusion: Our findings demonstrate that infection followed by immunization resulted in a higher antibody titer in a small cohort of mothers and their infants, respectively. Priming of the maternal immune system followed by boosting with immunization is required to induce a higher magnitude of SARS-CoV-2 specific antibodies in mothers resulting in increased passive transfer during pregnancy to their infants.