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Disclosures: The authors report no relevant financial disclosures.
September 22, 2021
2 min read

COVID-19 vaccination during pregnancy confers high levels of antibodies to infants

Disclosures: The authors report no relevant financial disclosures.
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Infants born to mothers who received the Pfizer-BioNTech or Moderna COVID-19 vaccine had high levels of protective antibodies, according to findings published in the American Journal of Obstetrics and Gynecology — Maternal Fetal Medicine.

“What’s new about this study is that we were able to demonstrate that the antibodies the mother builds to the vaccine cross the placenta and go to the baby, and have the potential of protecting the baby in the first days of life from getting SARS-CoV-2,” Ashley Roman, MD, director of the division of maternal fetal medicine in the department of obstetrics and gynecology at NYU Langone Health, told Healio Primary Care.
36 pregnant women who received at least one dose of either mRNA vaccine. They analyzed antibodies to the spike protein (anti-S IgG), which may be present after infection or vaccination, as well as antibodies to the nucleocapsid protein (anti-N IgG), which are only present after infection, according to the researchers. Umbilical cord blood samples with a reactivity of greater than or equal to 0.8 U/mL were considered positive for anti-S antibodies.

Graphical depiction of data presented in article
Trostle MD, et al. AJOG MFM. 2021;doi:10.1016/j.ajogmf.2021.100481.

The median age of the women during vaccination was 35.5 years. None of the participants previously had a known SARS-CoV-2 infection.

Ashley Roman

Among the 36 women, 72% received the Pfizer-BioNTech vaccine and 28% received the Moderna vaccine. Most women (83%) received the first dose of the vaccine during their second trimester, 6% received it during their first trimester and 11% during their third trimester. The median duration between completing the vaccine series and delivery was 13 weeks. One mother received her second vaccine dose after delivery. The median gestational age at delivery for the 36 infants was 39.1 weeks.

Evidence of high antibody levels

After delivery, the researchers reported that 100% of infants had anti-S IgG antibodies at high levels. Thirty-four of the 36 infants had titers greater than 250 U/mL, including the infant whose mother received only one dose of the vaccine prior to delivery. The remaining two infants had titers of 201 U/mL and 249 U/mL. Their mothers received the second vaccine dose during the first trimester, according to Roman and colleagues. Thirty-one of the 36 infants tested negative for anti-N IgG antibodies.

The lower antibody levels observed in infants born to mothers with longer latency between their last vaccination and delivery “suggest that cord blood antibody level may correlate with interval of time from vaccine administration to delivery,” the researchers wrote.

While the sample size was small, the results are encouraging, senior author Jennifer L. Lighter, MD, an associate professor in the department of pediatrics and a hospital epidemiologist at Hassenfeld Children’s Hospital at NYU Langone, said in a press release.

Jennifer L. Lighter

“High levels of transplacental antibody transfer are not surprising. It is consistent with what we see with other immunizations,” Lighter said.

Vaccinating pregnant women

According to CDC data, as of Sept. 11, 2021, only 30.1% of women had received a COVID-19 vaccine prior to or during pregnancy, despite evidence of prenatal safety. Healio Primary Care previously reported that antibodies can also be shared between a mother and baby through breast milk in lactating women who received the Pfizer-BioNTech vaccine.

“This study provides another compelling reason why pregnant women should be vaccinated,” Roman said. “It doesn't just help prevent severe illness in the mother, but it seems to provide some benefit to the babies after birth.”


COVID-19 vaccination among pregnant people aged 18-49 years overall, by race/ethnicity, and date reported to CDC - Vaccine Safety Datalink, United States. Accessed Sept. 21, 2021.

Pregnant women who receive COVID-19 vaccination pass protection from the virus to their newborns. Published Sept. 22, 2021. Accessed Sept. 22, 2021.

Trostle MD, et al. AJOG MFM. 2021;doi:10.1016/j.ajogmf.2021.100481.