mRNA COVID-19 Vaccine Generates Robust Response in Pregnant, Lactating Women

Researchers evaluated the immunogenicity and reactogenicity of COVID-19 mRNA vaccines in pregnant and lactating women compared with women who were not pregnant and those who were naturally infected with SARS-CoV-2 during pregnancy.

The COVID-19 mRNA vaccines provide robust immunity in pregnant and lactating women, similar to responses observed in nonpregnant women, according to results published in the American Journal of Obstetrics and Gynecology.

Study researchers recruited women (N=131) at or over the age of 18 at 2 tertiary care centers who were pregnant, lactating, or were nonpregnant and of reproductive age (18-45 years). Participants received either the BNT162b2 vaccine by Pfizer-BioNTech (pregnant, n=41; lactating, n=16; nonpregnant, n=8) or the mRNA-1273 vaccine by Moderna (pregnant, n=43; lactating, n=15; nonpregnant, n=8).

Immunoglobulin (Ig) G, IgM, and IgA responses to the SARS-CoV-2 spike and receptor binding domain were quantified in participant sera (n=131) and breastmilk (n=31) at baseline, after the second dose, 2 to 6 weeks after the second dose, and at delivery. Umbilical cord sera titers were also assessed at delivery in 10 participants. Titers were compared to pregnant women who tested SARS-CoV-2 positive during weeks 4 to 12 of their pregnancy.

Results indicated that when vaccinated, antibody titers were similar in pregnant (median, 5.59; interquartile range [IQR], 4.68-5.89) and lactating (median, 5.74; IQR, 5.06-6.22) women, compared with women who were not pregnant (median, 5.62; IQR, 4.77-5.98; P =.24). Higher levels of IgA were detected after the second dose in Moderna recipients, and robust IgG levels were noted in all vaccines. Similar to the influenza and pertussis vaccinations, vaccine-induced IgG was transferred across the placenta.

Women who were vaccinated during pregnancy had antibodies present in all breastmilk and umbilical cord samples, though titers in umbilical cord samples were lower compared to maternal sera (P =.05). Study researchers also saw improved transfer with increased time, indicating that neutralizing antibodies in the umbilical cord may be higher if the vaccine were given earlier during gestation.

Women who were vaccinated during pregnancy had higher titers compared with women who were naturally infected by SARS-CoV-2 during pregnancy (P <.0001).

Side effects of pregnant and lactating women receiving the COVID-19 vaccine were similar compared with nonpregnant women.

“These data provide a compelling argument that COVID-19 mRNA vaccines induce similar humoral immunity in pregnant and lactating women as in the [nonpregnant]  population,” the study authors concluded. However, “these data do not elucidate potential risks to the fetus.”


Gray KJ, Bordt EA, Atyeo C, et al. COVID-19 vaccine response in pregnant and lactating women: a cohort study. Am J Obstet Gynecol. Published online March 25, 2021. doi:10.1016/j.ajog.2021.03.023

This article originally appeared on Infectious Disease Advisor