Researchers say pregnant women should follow COVID-19 vaccine schedules for full antibody protection

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The two-dose immunization schedule for COVID-19 mRNA vaccines ultimately stimulates comparable antibody responses in pregnant, lactating, and nonpregnant women of reproductive age, but key antibody functions kick in more slowly in pregnant and lactating women following the first dose, according to new research by Massachusetts General Hospital investigators published in the journal Science Translational Medicine.

The research points to the importance of following the recommended timelines for the first and second dose of the COVID-19 mRNA vaccines in pregnant and lactating women to ensure full immunity.

The work looked specifically at the titers, Fc-receptor binding capacity, and functionality of individuals’ antibodies after COVID-19 vaccination. Fc-receptor binding capacity is the ability of antibodies to bind to Fc receptors present on immune cells and tissues. Fc-receptor binding is critical to activating cells in the fight against the virus that causes COVID-19, and at the placental tissue level, Fc-receptor binding plays a key role in the transfer of maternal antibodies to the fetus. The researchers found that Fc-receptor binding capacity and other key antibody functions developed more slowly in pregnant and lactating individuals than nonpregnant women, and the second vaccine dose was key to achieving full antibody binding and functionality.

The study also uncovered key differences between vaccine responses in pregnant and lactating individuals, highlighting the importance of including not only pregnant but also lactating individuals in vaccine studies. Specifically, lactating women had higher activity of natural killer cells after vaccination than pregnant women. These cells play a key role in the innate immune response by killing virally infected cells, the researchers said.

This latest study also revealed that the antibody responses induced by the mRNA-1273 (Moderna) and BNT162b2 (Pfizer-BioNTech) vaccines were different, with the Moderna-induced antibody response being more focused and coordinated in the study participants. However, the researchers said both vaccines induced highly effective antibody responses.