Pregnant women who have contracted the novel coronavirus have been shown to pass on protective antibodies to their newborns, according to a new study conducted by researchers at the Perelman School of Medicine at the University of Pennsylvania.

The findings, which were reported in JAMA Pediatrics, suggest that antibodies to SARS-CoV-2—the scientific name for the virus that causes COVID-19—are, in fact, able to cross the placenta in mothers who have had either symptomatic or asymptomatic exposure to the disease.

“This transfer appears to be pretty efficient,” the study’s senior co-author Dr. Karen Puopolo, a neonatologist at Children’s Hospital of Philadelphia and an associate professor at the University of Pennsylvania, said in a statement.

The researchers further revealed that the concentration of antibodies seen in the newborns’ blood was similar to the concentration found in their mothers’ blood—and, more surprisingly, there were some instances in which the newborn’s blood concentration of antibodies was higher than the mother’s.

“In general, our findings are consistent with what we know about cross-placental transfer of antibodies to other viruses, and should contribute to the discussion about whether and when to vaccinate pregnant women against SARS-CoV-2,” the study’s senor co-author Dr. Scott Hensley, an associate professor of microbiology at Penn Medicine, said in a statement.

For the study, the researchers tested blood samples from nearly fifteen hundred women and their newborns for the presence of antibodies to the coronavirus. The team eventually discovered that eighty-three of the women had significant levels of SARS-CoV-2-specific antibodies.

Moreover, the vast majority, 87 percent, of the newborns also showed significant levels of SARS-CoV-2-specific antibodies in samples of umbilical cord blood that were drawn at birth. The researchers noted that they found no evidence that the antibodies were due to any type of fetal infection—indicating that it is likely that the antibodies crossed the placenta from the mother’s blood.

Immunoglobulin G (IgG) antibodies, which are the most common class of antibodies found in the blood, appeared to transfer “readily” in high levels across the placenta.

“However, a class of larger antibodies, known as IgM antibodies, which tend to be produced earlier in an infection and are not known to cross the placenta, were not detected in any cord blood sample,” the study’s researchers wrote.

“Since infants have some ability to produce their own IgM antibodies, the absence of these antibodies also suggested that the SARS-CoV-2 virus itself had not crossed the placenta and infected them.”

Smaller studies in the past also have found evidence that maternal antibodies can cross the placenta to the fetal bloodstream. But the dynamics and the efficiency of such transfers have been mostly unclear.

Ethen Kim Lieser is a Minneapolis-based Science and Tech Editor who has held posts at Google, The Korea Herald, Lincoln Journal Star, AsianWeek, and Arirang TV. Follow or contact him on LinkedIn.

Image: Reuters.