Early Protection

Study supports safety of COVID-19 vaccines for pregnant, lactating women

Illustration of pregnant woman wearing a mask with green background of coronaviruses
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This article is part of Harvard Medical School’s continuing coverage of medicine, biomedical research, medical education, and policy related to the SARS-CoV-2 pandemic and the disease COVID-19.

Pregnant women with symptomatic COVID-19 face a greater risk of being admitted to the intensive care unit, are more likely to need mechanical ventilation, and are more likely to die, compared with nonpregnant reproductive-age women.

Increases in preterm birth and stillbirth have also been observed in pregnancies complicated by the viral infection. In light of this heightened risk, the U.S. Centers for Disease Control and Prevention recommends that those who are pregnant may choose to be vaccinated at their own discretion with their health care provider. However, pregnant and lactating women were not included in phase 3 vaccine efficacy trials, leading to a lack of data on vaccine safety and immunogenicity in this population. 

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Now, a small study by researchers at Harvard Medical School and Beth Israel Deaconess Medical Center adds to a growing body of research that COVID-19 vaccines are safe during pregnancy and will play an important role in disease prevention in pregnant women.  

The findings, published in JAMA, show that mRNA-based COVID-19 vaccines triggered immune responses in pregnant and lactating women. Further analyses also revealed that maternal vaccine antibodies are transferred into infant cord blood and breast milk.

“Our study supports the use of vaccines in pregnant and lactating individuals. The vaccine-elicited antibodies we detected in both infant cord blood and breast milk suggest that vaccinating pregnant mothers may potentially protect infants from COVID-19 infection,” said lead author Ai-ris Collier, HMS instructor in obstetrics, gynecology, and reproductive biology at Beth Israel Deaconess. “Future research should focus on determining the timing of vaccination that optimizes delivery of antibodies through the placenta and breast milk to newborns.” 

Collier and colleagues conducted an exploratory study of 103 women, ages 18 to 45, who received one of two mRNA COVID-19 vaccines (54 percent Pfizer and 46 percent Moderna). The scientists found similar levels of vaccine-induced antibody function and T cell responses in all nonpregnant, pregnant, and lactating women after their second vaccine dose. Additionally, both pregnant and nonpregnant women who received the mRNA vaccines developed cross-reactive immune responses against the COVID-19 variants of concern, B.1.1.7 and B.1.351.

“The COVID-19 mRNA vaccines raised robust immune responses in pregnant, lactating, and nonpregnant nonlactating women,” said senior corresponding author Dan Barouch, the HMS William Bosworth Castle Professor of Medicine and director of the Center for Virology and Vaccine Research.  “Additionally, the vaccine-elicited antibody responses were greater than antibody responses seen after COVID-19 infections. These findings add to the emerging data that support the use of these vaccines in pregnant and lactating women.” 

This work was supported by the National Institutes of Health (CA260476, AI146779), Massachusetts Consortium on Pathogen Readiness, Musk Foundation, Reproductive Scientist Development Program from the Eunice Kennedy Shriver National Institute of Child Health and Human Development, Burroughs Wellcome Fund (HD000849), Multidisciplinary AIDS Training Program (AI007387), Harvard Clinical and Translational Science Center (TR002541), and Ragon Institute of MGH, MIT, and Harvard.

Adapted from a Beth Israel Deaconess news release.