Moderna, Pfizer Vaccines Safe and Effective in Pregnant, Lactating Women

March 26, 2021

A team of researchers have released study results that show the Moderna and Pfizer vaccines are indeed safe and effective for this population.

Due to the omission of pregnant and lactating women in the initial trials, data were lacking for vaccine efficacy and infant humoral protection in this population, the research authors noted.

The study, funded by the National Institutes of Health (NIH), was released on Thursday and is the first of its kind that collected data for a large cohort on maternal antibody generation in response to COVID-19 vaccination, the authors noted. It is scheduled to appear in the American Journal of Obstetrics and Gynecology. Researchers compared vaccine-generated immunity to immunity gained from natural infection with the virus. In fact, pregnant women who received either of the vaccines elicited comparable humoral immune responses when compared to non-pregnant controls. They also generated higher antibody titers compared to those observed in those with actual COVID-19 infection in pregnancy. The antibodies were present in breastmilk and umbilical cord blood after vaccination.

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For the study, 131 productive-age vaccine recipients (84 pregnant, 31 lactating, and 16 non-pregnant) were enrolled in a prospective cohort study at two academic medical centers, the authors said. Titers of SARS-CoV-2 Spike and RBD IgG, IgA and IgM were quantified in participant sera (N=131) and breastmilk (N=31) at baseline, second vaccine dose, 2-6 weeks post second vaccine, and at delivery by Luminex. Umbilical cord sera (N=10) titers were assessed at delivery. Titers were compared to those of pregnant women 4-12 weeks from natural infection (N=37) by ELISA. A pseudovirus neutralization assay was used to quantify neutralizing antibody titers for the subset of women who delivered during the study period. Post-vaccination symptoms were assessed via questionnaire. Kruskal-Wallis tests and a mixed effects model, with correction for multiple comparisons, were used to assess differences between groups.

The authors, discussing the clinical implications, said that when considering vaccination in pregnancy, evidence regarding maternal and fetal benefit, as well as potential maternal and fetal harm and effects on pregnancy outcomes should be weighed carefully. “While the absolute risk of severe COVID-19 is low in pregnant women, pregnancy is a risk factor for severe disease,” they wrote. “There are well-documented maternal, neonatal, and obstetric risks of SARS-CoV-2 infection during pregnancy. These data provide a compelling argument that COVID-19 mRNA vaccines induce similar humoral immunity in pregnant and lactating women as in the non-pregnant population. These data do not elucidate potential risks to the fetus.”

Read more on Contemporary OB/GYN.


  1. Gray KJ, Bordt EA, Atyeo C, Deriso E, et al. COVID-19 vaccine response in pregnant and lactating women: a cohort study, American Journal of Obstetrics and Gynecology (2021), doi: https://