COVID-19 Vaccination of the Mother Protects the Fetus and Baby

American Journal of Obstetrics and Gynecology published a prospective cohort study on 25 March, according to which pregnant and breastfeeding women receiving mRNA COVID-19 vaccine developed a strong immune response and produced antibodies that could be transferred to the fetus through the placenta and to newborns through breast milk.

The findings showed that this group's antibody response to vaccination was greater than that in women who had COVID-19 infection during pregnancy. Although the researchers detected antibodies in umbilical cord blood and infant milk against SARS-CoV-2(the novel coronavirus), it is not yet known how much protection these antibodies may provide to newborns.

Dr. Kathryn J. Gray from Harvard Medical School and colleagues from the Department of Obstetrics and Gynecology at Brigham and Women’s Hospital: “The presence of neutralizing antibody transfer in nearly all cords, and improved transfer with increasing time from vaccination, point to the promise of providing immunity to newborns with an mRNA vaccine.” they wrote. “Transfer could probably be optimized if vaccination is given early in pregnancy, but this needs to be examined directly in future studies.”

The researchers followed 84 pregnant women, 31 breastfeeding women, and 16 nonpregnant women who received a COVID-19 vaccine. Titers of IgA, IgG, and IgM antibodies against the SARS-CoV-2 spike protein, receptor-binding domain (RBD), and the S1 and S2 components of the spike were measured 4 times in the blood of 131 participants and in the breast milk of breastfeeding women: at baseline, when they received the second vaccine dose, 2-6 weeks after their second dose, and at delivery for the 13 women who gave birth during the study period.

The study group included healthcare workers and was predominantly white and non-Hispanic. In addition, two pregnant women, two breastfeeding women, and one nonpregnant woman in the study had previously had SARS-CoV-2 infection.

Most pregnant women received the vaccine in the second (46%) or third (40%) trimester. Women in all three groups — pregnant, breastfeeding, and nonpregnant — experienced similar side effects from each vaccine dose, including fever / chills in 32% of pregnant women and half of nonpregnant women after the second dose.

Vaccine-induced antibody levels were similar among pregnant, breastfeeding, and nonpregnant women, and the levels did not differ according to the trimester in which women received the vaccine. The researchers then compared antibody levels from vaccine recipients with titers from 37 pregnant women obtained 4-12 weeks after a natural SARS-CoV-2 infection. Vaccine-induced antibody levels were significantly higher than those measured in women with natural infection during pregnancy (P <.001).

Below, to help better understand antibody responses, the changes over time in the short- and long-term antibodies developed by our immune system during mild COVID-19 can be seen:

The researchers identified IgG, IgA, and IgM antibodies in breast milk samples, including an increase in IgG antibodies after the second vaccine dose compared with baseline. The researchers said, "However, it remains unclear whether these antibodies are transferred 'efficiently' to infants".

The researchers found vaccine-induced antibodies in all 10 umbilical cord blood samples tested, all but one of which had been exposed to two vaccine doses.

"The cord with the lowest IgG against the spike (spike protein) and receptor-binding domain belonged to a mother who delivered between the first and second vaccine doses and had received her first dose 17 days before delivery, suggesting that 2 doses may be necessary to optimize transfer of humoral immunity to the newborn,” the researchers wrote. "Based on what is known about other vaccines, the amount of maternal IgG transferred across the placenta to the cord will probably differ according to the trimester of vaccination."

Although umbilical cord blood had lower neutralizing antibody titers than maternal blood, the difference was not significant (median interquartile range 52.3 versus 104.7, P = .05). The two cord blood samples without neutralizing antibodies came from a woman who had not received the second dose and a woman who received it 1 week before delivery.

"These data provide a compelling argument that COVID-19 mRNA vaccines induce similar humoral immunity in pregnant and breastfeeding women as in nonpregnant women" the researchers wrote. "These data do not explain the potential risks to the fetus."

What is important about these findings is that COVID vaccines are immunogenic in pregnant women. They may benefit newborns because antibodies cross the placenta. The main remaining questions are the safety of vaccination during pregnancy and its effectiveness during pregnancy.

We expect to see more studies on the safety and effectiveness of COVID-19 vaccines during pregnancy. Despite more than 73,600 infections due to COVID-19 and 80 deaths among pregnant people in the United States alone, none of the initial COVID-19 vaccine trials included pregnant or breastfeeding participants.

Prof. Dr. Linda Eckert, who specializes in maternal immunity in the Department of Obstetrics and Gynecology at the University of Washington in Seattle: "This is an important initial study to confirm antibody production following mRNA vaccination in pregnant women and antibody passage through cord blood and breast milk" she said. "Further studies are important to look at the timing of vaccination during pregnancy and whether it affects the level of antibodies passing to the fetus."

In an interview, Eckert said, "Although this is not a safety study, it does not show an increase in expected vaccine reactions, such as pain and fever, in pregnant compared with nonpregnant patients," she said. "This study cannot assess pregnancy outcomes, but it shows that pregnant women vaccinated with mRNA vaccines receive protection from the vaccine and that protection passes to the fetus through cord blood and to the baby through breast milk."

The research was funded by the Gates Foundation, the Massachusetts Consortium on Pathogen Readiness (MassCPR), the Musk Foundation, the Ragon Institute of MGH and MIT, and the National Institutes of Health together with Massachusetts General Hospital and Brigham and Women's Hospital.

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