COVID-19 vaccines effective in pregnant and lactating women

The new mRNA novel coronavirus (COVID-19) vaccines are highly effective in producing antibodies against the SARS-CoV-2 virus in pregnant and lactating women and confer protective immunity to newborns through breastmilk and the placenta, according to a new study by researchers at Massachusetts General Hospital (MGH), Brigham and Women's Hospital, and the Ragon Institute of MGH, published in the American Journal of Obstetrics and Gynecology (AJOG).

The cohort study looked at 131 women of reproductive age, 84 pregnant, 31 lactating and 16 non-pregnant, all of whom received one of the two new mRNA vaccines, Pfizer and BioNTech or Moderna. The vaccine-induced titers, or antibody levels, were equivalent in all three groups, the study found. Additionally, side effects after vaccination were rare and comparable across the study participants.

According to the U.S. Centers for Disease Control and Prevention (CDC), individuals who are pregnant are more likely to become severely ill with COVID-19, require hospitalization, intensive care, or ventilation, and may be at increased risk for adverse pregnancy outcomes. The researchers also compared vaccination-induced antibody levels to those induced by natural infection with COVID-19 in pregnancy and found significantly higher levels of antibodies from vaccination.

Vaccine-generated antibodies were also present in all umbilical cord blood and breastmilk samples taken from the study, showing the transfer of antibodies from mothers to newborns, the researchers said.

The study was also able to provide insight into potential differences between the immune response elicited by the Pfizer vaccine compared to the Moderna vaccine, finding the levels of mucosal (IgA) antibodies were higher after the second dose of Moderna compared to the second dose of Pfizer.

"This news of excellent vaccine efficacy is very encouraging for pregnant and breastfeeding women, who were left out of the initial COVID-19 vaccine trials," said Andrea Edlow, MD, MSc, co-senior author of the study, a maternal-fetal medicine specialist at MGH, and director of the Edlow Lab in the Vincent Center for Reproductive Biology, in a statement. "Filling in the information gaps with real data is key - especially for our pregnant patients who are at greater risk for complications from COVID-19. This study also highlights how eager pregnant and lactating individuals are to participate in research."

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