Vaccination from the early second trimester onwards gives a robust SARS-CoV-2 antibody response throughout pregnancy and provides antibodies for the neonate.

• Vaccination >16 weeks of gestation provides antibodies for both the mother and the neonate. • Antibodies in human milk after vaccination against SARS-CoV-2 during pregnancy. • High virus neutralization observed in mother-infant dyads. Preventive measures against COVID-19 are essential for pregnant women. Pregnant women are particularly vulnerable to emerging infectious pathogens due to alterations in their physiology. We aimed to determine the optimum timing of vaccination to protect pregnant women and their neonates from COVID-19. A prospective observational longitudinal cohort study in pregnant women who received COVID-19 vaccination. We collected blood samples to evaluate levels of antispike, receptor binding domain and nucleocapsid antibodies against SARS-CoV-2 before vaccination and 15 days after the first and second vaccination. We determined the neutralizing antibodies from mother-infant dyads in maternal and umbilical cord blood at birth. If available, immunoglobulin A was measured in human milk. We included 178 pregnant women. Median antispike immunoglobulin G levels increased significantly from 1.8 to 5431 binding antibody units/ml and receptor binding domain from 6 to 4466 binding antibody units/ml. Virus neutralization showed similar results between different weeks of gestation at vaccination (P >0.3). We advise vaccination in the early second trimester of pregnancy for the optimum balance between the maternal antibody response and placental antibody transfer to the neonate. [ABSTRACT FROM AUTHOR]