Research In Practice Blog

Maternal Fetal Antibody Transfer and COVID-19
Maternal Fetal Antibody Transfer and COVID-19

What we’ve learned about maternal fetal antibody transfer after COVID-19 vaccination vs. after natural infection

When COVID-19 vaccines first became available, information regarding their use and the appropriate timing of vaccination during pregnancy was limited. Our research team had already studied the placental transfer of COVID antibodies after maternal infection (Flannery DD, et al. JAMA Pediatr 2021), so we aimed to fill that knowledge gap.

Does Placental Antibody Transfer differ in patients who have received the COVID-19 vaccination and those who had the SARS-CoV-2 infection?

When a pregnant person is exposed to SARS-CoV-2, antibodies to the virus develop and can be transferred across the placenta to the newborn during pregnancy. The CDC recommends that pregnant people receive the COVID-19 vaccine because pregnancy is a risk factor for severe SARS-CoV-2 infection. In our study, published recently in JAMA Network Open, we used data from a large cohort of pregnant persons and their newborns to assess whether placental antibody transfer after COVID-19 vaccination is different from that after natural SARS-CoV-2 infection.

A total of 585 pregnant persons that gave birth at Pennsylvania Hospital between August 9, 2020, and April 25, 2021 and had SARS-CoV-2 antibodies detected in their blood at the time of delivery were included in this study.

Of those 585 patients with detectable antibodies, 169 had been vaccinated but never infected, and 408 had been naturally infected but not vaccinated. In order to compare infection vs vaccination, we excluded 8 individuals who had been both vaccinated and infected. Maternal antibody concentration of the vaccine recipients was ~10-fold higher than that of the patients with a history of infection.

Analyzing Our Findings

When we evaluated the umbilical cord blood of the 585 deliveries, we found detectable SARS-CoV-2 antibodies in more than 95% of the infants, as well as evidence that placental transfer occurred as early as 26 weeks’ gestation. The levels of antibodies in the cord blood of infants born to vaccine recipients was also ~10 times higher than the levels of those born to mothers with infection.

Placental transfer ratios, however, were lower after vaccination compared with infection. We analyzed a variety of factors that might influence the transfer ratio, such as presence of maternal symptoms, vaccine type, gestational age at delivery, and vaccine timing during pregnancy.

We determined that the most significant factor associated with placental transfer was time from either vaccine or infection to delivery. An increase in placental antibody transfer ratio was found with longer duration of time between exposure and delivery. Cord blood antibodies were detectable as soon as 15 days after the first dose of an mRNA vaccine, and transfer ratios increased for several weeks after the first vaccine dose.

These findings suggest that although COVID-19 vaccination should be prioritized at any point in the pregnancy to protect the mother, pregnant persons should be encouraged to receive an mRNA vaccine at least a few weeks before delivery to ensure maximal placental antibody transfer and potentially maximize infant protection.


Dustin Flannery, DO, MSCE, is an attending physician at Children’s Hospital of Philadelphia and CHOP Newborn Care at Pennsylvania Hospital, an Assistant Professor of Pediatrics at the Perelman School of Medicine at the University of Pennsylvania, and a core faculty member in the Clinical Futures, a CHOP Research Institute Center of Emphasis. He is a graduate of the Pediatric Hospital Epidemiology and Outcomes Research Training (PHEOT) program managed by the Clinical Futures, and the Master of Science in Clinical Epidemiology (MSCE) program at the University of Pennsylvania.

Madeline Pfeifer, is a Clinical Research Coordinator at Children’s Hospital of Philadelphia and on the CHOP/Penn Perinatal Infectious Diseases Team.

Study authors from Children’s Hospital of Philadelphia and the University of Pennsylvania include Dustin D. Flannery, Sigrid Gouma, Miren B. Dhudasia, Sagori Mukhopadhyay, Madeline R Pfeifer, Emily C Woodford, Sara M Briker, Jourdan E Triebwasser, Jeffrey S. Gerber, Jeffrey S Morris, Madison E Weirick, Christopher M McAllister, Scott E Hensley, and Karen M Puopolo.

Corresponding Senior Author: Karen M. Puopolo, MD, PhD, Children's Hospital of Philadelphia

This study was supported/funded in part by a Foerderer Grant for Excellence from the Children’s Hospital of Philadelphia to principal investigators Karen Puopolo, MD, PhD and Dustin Flannery, DO, MSCE.

Flannery et al. "Comparison of Maternal and Neonatal Antibody Levels After COVID-19 Vaccination vs SARS-CoV-2 Infection," JAMA Network Open, November 9, 2022, DOI: 10.1001/jamanetworkopen.2022.40993