The findings of a new study support a growing amount of evidence that suggests pregnant women who contract the novel coronavirus pass protective antibodies to their newborns.
A study conducted by researchers at the Perelman School of Medicine at the University of Pennsylvania found antibodies to SARS-CoV-2, the scientific name for the virus that causes COVID-19, can cross the placenta in mothers who have had COVID-19 — but also in cases when the mother only had asymptomatic exposure to the virus.
What’s more, the researchers said, the concentration of antibodies found in the newborns’ blood was similar to the concentration found in their mothers’ blood, and there were times when the newborn’s blood concentration of SARS-CoV-2 antibodies was higher than its mother's.
The researchers also found that women who were infected with the novel virus earlier on in their pregnancy passed even more antibodies to their fetus when compared to those who were infected later on.
The study, published in JAMA Pediatrics, could help to clarify when pregnant women should receive the COVID-19 vaccine, the researchers said.
"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," said co-senior author Scott Hensley, Ph.D., in a statement. Hensley is also an associate professor of Microbiology at Penn Medicine and a member of the Penn Institute for Immunology.
For the study, researchers look for evidence of antibodies in blood samples taken from more than 1,400 women and their newborns. They found that 83 women had "significant levels" of SARS-CoV-2 antibodies, with 87% of these newborns also showing significant levels of these antibodies in blood samples taken from the umbilical cord when they were born.
"The study found no evidence that the antibodies were due to fetal infection, indicating that it is likely the antibodies crossed the placenta from the mother’s blood to the fetal circulation," reads a university news release on the findings.
Immunoglobulin G (IgG) antibodies — the most common class of antibodies in the blood — appeared to transfer "readily" across the placenta, with levels of these specific antibodies in the newborns being on par with those found in their mothers.
"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 researchers noted. "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."
"This transfer appears to be pretty efficient. In some of the cases, the newborn’s blood concentration of SARS-CoV-2 antibodies was even higher than the mother’s," said study co-senior author Karen Puopolo, MD, Ph.D., a neonatologist at Children’s Hospital of Philadelphia, an associate professor of Pediatrics at the University of Pennsylvania Perelman School of Medicine and Chief of the Section on Newborn Medicine at Pennsylvania Hospital, in a statement.
The team’s findings support past evidence that pregnant women may pass protective coronavirus antibodies to their fetuses. In December, for example, a study out of Singapore found that five babies born to mothers who had COVID-19 while they were pregnant were born with antibodies against the virus.
Studies about the effects COVID-19 may have on those who are pregnant and their babies are ongoing, with a recently-published National Institutes of Health-funded study suggesting that pregnant women who contract severe COVID-19 disease face a heightened risk of death and preterm delivery compared to those with asymptomatic cases of the illness. These findings furthered similar conclusions made by researchers from the Centers for Disease Control and Prevention (CDC) in November.
The CDC and the World Health Organization both recommend that pregnant women should receive a COVID-19 vaccine, with the latter recently reversing its stance on this ongoing debate.
While neither the Moderna vaccine nor the one created by Pfizer-BioNTech was approved specifically for use in pregnant women, "No safety concerns were demonstrated in rats that received [the] Moderna COVID-19 vaccine before or during pregnancy," the CDC notes on its website, adding that studies of the Pfizer-BioNTech vaccine on this topic are "ongoing."