Antibodies against SARS-CoV-2 cross the placenta during pregnancy and are detectable in most newborns born to mothers who had COVID-19 during pregnancy, according to findings from a study presented Jan. 28 at the meeting sponsored by the Society for Maternal-Fetal Medicine.
“I think the most striking finding is that we noticed a high degree of neutralizing response to natural infection even among asymptomatic infection, but of course a higher degree was seen in those with symptomatic infection,” Naima Joseph, MD, MPH, of Emory University, Atlanta, said in an interview.
“Our data demonstrate maternal capacity to mount an appropriate and robust immune response,” and maternal protective immunity lasted at least 28 days after infection, Dr. Joseph said. “Also, we noted higher neonatal cord blood titers in moms with higher titers, which suggests a relationship, but we need to better understand how transplacental transfer occurs as well as establish neonatal correlates of protection in order to see if and how maternal immunity may also benefit neonates.”
The researchers analyzed the amount of IgG and IgM antibodies in maternal and cord blood samples prospectively collected at delivery from women who tested positive for COVID-19 at any time while pregnant. They used enzyme-linked immunosorbent assay to assess for antibodies for the receptor binding domain of the SARS-CoV-2 spike protein.
The 32 pairs of mothers and infants in the study were predominantly non-Hispanic Black (72%) and Hispanic (25%), and 84% used Medicaid as their payer. Most of the mothers (72%) had at least one comorbidity, most commonly obesity, hypertension, and asthma or pulmonary disease. Just over half the women (53%) were symptomatic while they were infected, and 88% were ill with COVID-19 during the third trimester. The average time from infection to delivery was 28 days.
All the mothers had IgG antibodies, 94% had IgM antibodies, and 94% had neutralizing antibodies against SARS-CoV-2. Among the cord blood samples, 91% had IgG antibodies, 9% had IgM antibodies, and 25% had neutralizing antibodies.
“It’s reassuring that, so far, the physiological response is exactly what we expected it to be,” Judette Louis, MD, MPH, an associate professor of ob.gyn. and the ob.gyn. department chair at the University of South Florida, Tampa, said in an interview. “It’s what we would expect, but it’s always helpful to have more data to support that. Otherwise, you’re extrapolating from what you know from other conditions,” said Dr. Louis, who moderated the oral abstracts session.
Symptomatic infection was associated with significantly higher IgG titers than asymptomatic infection (P = .03), but no correlation was seen for IgM or neutralizing antibodies. In addition, although mothers who delivered more than 28 days after their infection had higher IgG titers (P = .05), no differences existed in IgM or neutralizing response.
Infants’ cord blood titers were significantly lower than their corresponding maternal samples, independently of symptoms or latency from infection to delivery (P < .001), Dr. Joseph reported.
“Transplacental efficiency in other pathogens has been shown to be correlated with neonatal immunity when the ratio of cord to maternal blood is greater than 1,” Dr. Joseph said in her presentation. Their data showed “suboptimal efficiency” at a ratio of 0.81.
The study’s small sample size and lack of a control group were weaknesses, but a major strength was having a population at disproportionately higher risk for infection and severe morbidity than the general population.