SARS-CoV-2 antibodies transferred across the placenta in 87% of pregnant women who had COVID-19 at some point, suggesting that newborns of seropositive mothers may have some protection against the novel coronavirus at birth, according to a study today in JAMA Pediatrics. However, a second, unpublished study suggests that the maternal-infant antibody transfer is lower than expected.
The amount and nature of the antibodies in the newborns depended on the type and quantity of antibodies that were present in the mother during her pregnancy.
According to the researchers of the study, “Our findings demonstrate the potential for maternally derived antibodies to provide neonatal protection from SARS-CoV-2 infection and will help inform both neonatal management guidance and design of vaccine trials during pregnancy.”
IgG but not IgM in cord blood:
Immunoglobulin G (IgG) is a type of antibody found in the cord blood that helps protect the body from various infections.
As per the recent study, immunoglobulin G (IgG) were detected in 83 of 1,471 women (6%) at delivery, and IgG was found in cord blood from 72 of 83 of the newborns (87%). This reflected a similar level of IgG present in the mother and the newborn.The 11 babies who tested negative for the antibodies were either due to the low levels of IgG levels in their mothers or due to the low amount of antibody production by the mothers.
On the contrary, no IgM antibodies, which are the first antibody to appear in the response to initial exposure to an antigen, were found in cord blood of the mothers, indicating that the mother did not infect their child during pregnancy as IgM antibodies cannot be transferred through the placenta.
That said, according to the researchers, “Further studies are needed to determine if SARS-CoV-2 antibodies are protective against newborn infection; if so, at what concentration; and whether the transplacental kinetics of vaccine-elicited antibodies are similar to naturally acquired antibodies.”