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Clinical Context

The primary goal of vaccinations administered during pregnancy is to protect the mother from serious illness. Transplacental antibody transfer could also protect newborns, but some women have unfounded concerns regarding the safety of the COVID-19 vaccine during pregnancy.

Study Synopsis and Perspective

Women who receive COVID-19 vaccines during pregnancy pass antibodies to their babies, which could protect newborns from the disease, research has shown.

In a new study that examines umbilical cord blood from 36 deliveries, researchers provide additional evidence that vaccines -- and not COVID-19 -- elicited the antibodies detected in this cohort.

Researchers with New York University (NYU) Langone Health conducted a study that included pregnant women who had received at least 1 dose of a messenger RNA (mRNA) COVID-19 vaccine (Pfizer-BioNTech or Moderna) by June 4.

All neonates had antibodies to the spike protein at high titers, the researchers found.

Unlike similar prior studies, the researchers also looked for antibodies to the nucleocapsid protein, which would have indicated the presence of antibodies from natural COVID-19. They did not detect antibodies to the nucleocapsid protein, and the lack of these antibodies suggests that the antibodies to the spike protein resulted from vaccination and not from prior infection, the researchers said.

The participants had a median time from completion of the vaccine series to delivery of 13 weeks. The study was published online in the American Journal of Obstetrics & Gynecology MFM.^[1]

"The presence of these anti-spike antibodies in the cord blood should, at least in theory, offer these newborns some degree of protection," said study investigator Ashley S. Roman, MD, director of the division of maternal-fetal medicine at NYU Langone Health. "While the primary rationale for vaccination during pregnancy is to keep moms healthy and keep moms out of the hospital, the outstanding question to us was whether there is any fetal or neonatal benefit conferred by receiving the vaccine during pregnancy."

Questions remain about the degree and durability of protection for newborns from these antibodies. An ongoing study, MOMI-VAX,^[2] aims to systematically measure antibody levels in mothers who receive COVID-19 vaccines during pregnancy and in their babies over time.

The present study contributes welcome preliminary evidence suggesting a benefit to infants, said Emily Adhikari, MD, of The University of Texas Southwestern Medical Center in Dallas, Texas, who was not involved in the study.

Still, "the main concern and our priority as obstetricians is to vaccinate pregnant women to protect them from severe or critical illness," she said.

Although most individuals infected with SARS-CoV-2 recover, a significant portion of pregnant women get seriously sick, Adhikari said. "With this recent Delta surge, we are seeing more pregnant patients who are sicker," said Adhikari, who has published research from one hospital describing this trend.^[3]

When weighing whether patients should receive COVID-19 vaccines in pregnancy, the risks from infection have outweighed any risk from vaccination to such an extent that there is "not a comparison to make," Adhikari said. "The risks of the infection are so much higher.

"For me, it is a matter of making sure that my patient understands that we have really good safety data on these vaccines and there is no reason to think that a pregnant person would be harmed by them. On the contrary, the benefit is to protect and maybe even save your life," Adhikari said, "[a]nd now we have more evidence that the fetus may also benefit."

The rationale for vaccinations during pregnancy can vary, Roman said. Flu shots in pregnancy are intended to protect the mother, although they confer protection for newborns as well. With the whooping cough vaccine given in the third trimester, however, the primary aim is to protect the baby from whooping cough in the first months of life, Roman said.

"I think it is really important for pregnant women to understand that antibodies crossing the placenta is a good thing," she added.

As patients who already have received COVID-19 vaccines become pregnant and may become eligible for a booster dose, Adhikari will offer it, she said, though she has confidence in the protection provided by the initial immune response.

Roman and Adhikari had no disclosures.

Clinical Implications

• mRNA COVID-19 vaccination during pregnancy results in transplacental antibody transfer.
• Positive anti-S IgG and negative anti-N IgG in cord blood reflect vertical transfer of antibodies from maternal vaccination rather than natural infection.
• Implications for the Healthcare Team: These study findings add novel support for providing education to and vaccinating pregnant women, including neonatal benefit and potential protection from COVID-19 illness in the first days of life.

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