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In the United States alone as of March 1, 2021, more than 73,600 infections have affected pregnant women and 80 of these women died. With the emergence of the coronavirus disease in late 2019, scientists carried out vaccine studies on people of many ages, but excluded pregnant and lactating women.

Scientists at Massachusetts General Hospital and Brigham and Women’s Hospital investigated the effectiveness of the mRNA vaccine (developed by companies Pfizer/BioNTech and Moderna) in pregnant and lactating women. Both of these vaccines use mRNA to introduce the SARS-CoV-2 spike antigen to the immune system without causing infection. The scientists hypothesized that vaccination would be safe and effective for pregnant women. Newborns may be able to acquire immunity in utero and from breast milk, but that is not yet known for the mRNA vaccines.

One hundred and thirty one women took part in this study. Of these women, 84 were pregnant, 31 were lactating, and 16 were not pregnant. They recorded the side effects that vaccinations could cause. The number of women with side effects after the first vaccine was low, this number was slightly higher after the second dose.

Antibodies such as IgG, IgA, and IgM are substances produced by the body to fight foreign organisms such as viruses that have entered the body. In other studies, the Pfizer and Moderna vaccines have increased the levels of natural antibodies IgG and IgA over time. This is the first published observation that vaccination is safe and effective for pregnant women, but there have been no studies yet on safety in infants.

Additionally, it is unknown if antibodies to the virus are passed from mother to baby. Scientists took samples of breast milk to answer this question. Surprisingly, there were no increases in IgA and IgM levels in these samples, indicating that breast milk may not be a significant source of antibodies for the infant. However, there were high levels of IgG in breast milk, suggesting that it can transfer IgG antibodies. They say the failure to detect IgA may be due to the intramuscular administration of the vaccine.

This study concluded that mRNA vaccines do not pose any threat to the health of pregnant and lactating women and that breast milk transfers high IgG levels to the newborn, but not necessarily IgM and IgA antibodies.

Scientists said that this situation may be because the vaccination is done intramuscularly, which takes a bit longer to reach the bloodstream. After the boost, scientists noted that IgA levels in pregnant and lactating women who received the Moderna vaccine had increased. The scientists suggested that earlier vaccination during pregnancy could result in increased IgA levels. But another study did not support this recommendation. They observed a high increase in IgG levels in that study. Breast milk IgG plays an important role in immunity against many vaccinable infections such as HIV and influenza.

An application called V-safe has been developed to track Covid-19 vaccinations. This application allows you to enter the side effects that may occur after vaccination into the system personally. This way, you can report your post-vaccination status to the CDC. The researchers compared their results to this larger dataset to see if their results were an anomaly or consistent with existing data. Fortunately, the results were consistent. Pregnant women did not react any differently to the vaccine than non-pregnant women between ages 16-54.

There are many more things to consider besides immunity, say the authors, when it comes to vaccine safety. They stress that studies are needed in larger populations, involving other types of immunity, and with longer follow-up to assess risks to the mother and fetus. So far, the mRNA vaccine platform appears to be moving in a positive direction.

Study Information

Original study: Coronavirus disease 2019 vaccine response in pregnant and lactating women: a cohort study

Study published on: Spring 2021

Study author(s): Kathryn J. Gray, Evan A. Bordt, Caroline Atyeo, Elizabeth Deriso, Babatunde Akinwunmi, Nicola Young, Aranxta Medina Baez, Lydia L. Shook, Dana Cvrk, Kaitlyn James, Rose De Guzman, Sara Brigida, Khady Diouf, Ilona Goldfarb, Lisa M. Bebell, Lael M. Yonker, Alessio Fasano, S. Alireza Rabi, Michal A. Elovitz, Galit Alter, Andrea G. Edlow

The study was done at: Massachusetts General Hospital, Brigham and Women’s Hospital

The study was funded by: National Institutes of Health, The Gates Foundation, the Massachusetts Consortium on Pathogen Readiness; the Musk Foundation; the Ragon Institute of Massachusetts General Hospital, Massachusetts Institute of Technology, and the Massachusetts General Hospital; and Brigham and Women’s Hospital Departments of Obstetrics and Gynecology.

Raw data availability: A lot of it was provided in the paper and supplemental information

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