Anti-Severe Acute Respiratory Syndrome Coronavirus 2 IgG Is Present in the Amniotic Fluid of both Infected and Vaccinated Women at Second Trimester of Pregnancy: A Cohort Study

<b><i>Introduction:</i></b> Pregnant women are protected from the complications of COVID-19 infection, thanks to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) vaccination. The benefit of this vaccination to prevent morbidity and mortality in the fetus has not yet been completely elucidated. Our aim was to test the presence of anti-SARS-CoV-2 antibodies in the amniotic fluid during the second trimester of pregnancy and then to compare them to the antibody levels in maternal serum to evaluate their correlation and to improve amniotic fluid immunological characteristics knowledge. <b><i>Methods:</i></b> This cohort study took place at the Policlinico G. Martino of Messina from September 2021 to February 2022; 22 pregnant women had amniocentesis: we analyzed serum and amniotic fluid samples of women who contracted the SARS-CoV-2 infection or vaccinated against the same virus within 1 year, and women never infected or vaccinated against it. Amniotic fluids and peripheral blood were collected to evaluate IgG anti-SARS-CoV-2 nucleocapsid and spike S1 protein antibodies. <b><i>Results:</i></b> Patients vaccinated had higher S1 receptor-binding domain antibody levels both in amniotic fluid (<i>p</i> &lt; 0.006; mean 68.70; standard deviation [SD] 85.46) and maternal blood (<i>p</i> &lt; 0.005; mean 1989.86; SD 3777.15) than unvaccinated women. Anti-nucleocapsid antibodies were present in women who developed COVID infection both in amniotic fluid and maternal blood but not in unvaccinated women. There was a high correlation between the concentrations of anti-spike antibody levels in serum and amniotic fluid of vaccinated women (<i>p</i> &lt; 0.001; <i>R</i> = 1.0) and of anti-nucleocapsid antibody levels in serum and amniotic fluid of women who developed COVID infection (<i>p</i> &lt; 0.001; <i>R</i> = 0.93). <b><i>Conclusion:</i></b> Recent studies have shown that SARS-CoV-2 vaccination during pregnancy is safe. Moreover, we can assume that there is an early transplacental antibody transfer after anti-SARS-CoV-2 immunization to protect the fetus, and there is also a high correlation between levels of anti-nucleocapsid antibodies in blood and amniotic fluid of pregnant women previously infected.