COVID mRNA vaccines induce immune response in pregnant, lactating women

COVID-19 mRNA vaccines trigger an immune response in pregnant and breastfeeding women, and maternal antibodies transfer into infant cord blood and breast milk, a small descriptive study yesterday in JAMA finds.

A team led by Beth Israel Deaconess Medical Center researchers in Boston assessed immune response in a convenience sample of 103 pregnant, lactating, and nonpregnant women given either the Pfizer/BioNTech (54%) or the Moderna (46%) COVID-19 vaccine from December 2020 through March 2021. Seventeen percent of pregnant participants received their first vaccine dose in the first trimester, while 50% received it in their second trimester, and 33% got theirs in their final trimester.

The researchers compared their immune responses to those of 22 pregnant and 6 nonpregnant women who had confirmed COVID-19 infection from April 2020 through March 2021. Median time from coronavirus symptom onset to serum sample collection was 12 days in nonpregnant women and 41 days for pregnant participants.

The nine pregnant women who delivered during the study contributed infant cord blood, and previous COVID-19 infection was identified in 4% of vaccinated participants. All women were aged 18 to 45 years, and 66% were White.

Cross reactivity against B117, B1351

Levels of vaccine-induced antibody function and T cell responses were similar in all 30 pregnant, 16 lactating, and 57 nonpregnant women 2 to 8 weeks after they received their second dose of vaccine, and their immune responses were stronger than that triggered by natural coronavirus infection.

Binding and neutralizing and functional nonneutralizing coronavirus antibodies and CD4 and CD8 T cells were observed in all study participants, and binding and neutralizing antibodies were also detected in infant cord blood and breast milk.

Both vaccinated pregnant and nonpregnant women also had cross-reactive immune responses against the SARS-CoV-2 variants B117 (first seen in England) and B1351 (first identified in South Africa). Although concentrations of neutralizing antibodies against the variants in maternal serum and infant cord blood were reduced, nonneutralizing antibody binding and T cell responses in both pregnant and nonpregnant women were not significantly depressed.

"These data suggest that there may be greater cross-reactivity for functional nonneutralizing antibodies and cellular immune responses than for neutralizing antibodies against SARS-CoV-2 variants of concern," the authors said. "The mechanistic roles of these different immune responses in protecting against COVID-19 infection and disease remain to be determined, but data from nonhuman primates suggest that both humoral and cellular immune responses may contribute to protection."

The most common vaccine-related side effect after the second dose was fever, reported by 14% of pregnant women, 44% of breastfeeding women, and 52% of nonpregnant women. No severe adverse effects or pregnancy or neonatal complications were reported.

Determining optimal timing of vaccinations

The results are important, the researchers said, because pregnant women with symptomatic COVID-19 are at higher risk for death, intensive care unit admission, and mechanical ventilation than their nonpregnant peers. Likewise, preterm births and stillbirths have been noted in cases of maternal COVID-19 infection, although maternal-fetus coronavirus transmission has been rare, and newborns gain passive immunity via placental antibody transfer and breast milk after natural maternal infection.

The Centers for Disease Control and Prevention recommends that pregnant women talk with their healthcare provider about whether COVID-19 vaccination is right for them. The authors, however, noted that pregnant and lactating women weren't included in phase 3 vaccine efficacy trials and thus data on vaccine immune responses and safety in that group are lacking.

Lead study author Ai-ris Collier, MD, said in a Beth Israel Deaconess press release that the study supports COVID-19 vaccination in pregnant and breastfeeding women and that the presence of coronavirus antibodies in infant cord blood and breast milk suggest that maternal vaccination may protect infants from infection. "Future research should focus on determining the timing of vaccination that optimizes delivery of antibodies through the placenta and breast milk to newborns," she said.

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