Implications for maternal COVID-19 vaccination
Although the data are not yet available, Dr. Joseph said they have expanded their protocol to include vaccinated pregnant women.
“The key to developing an effective vaccine [for pregnant people] is in really characterizing adaptive immunity in pregnancy,” Dr. Joseph told SMFM attendees. “I think that these findings inform further vaccine development in demonstrating that maternal immunity is robust.”
The World Health Organization recently recommended withholding COVID-19 vaccines from pregnant people, but the SMFM and American College of Obstetricians and Gynecologists subsequently issued a joint statement reaffirming that the COVID-19 vaccines authorized by the FDA “should not be withheld from pregnant individuals who choose to receive the vaccine.”
“One of the questions people ask is whether in pregnancy you’re going to mount a good response to the vaccine the way you would outside of pregnancy,” Dr. Louis said. “If we can demonstrate that you do, that may provide the information that some mothers need to make their decisions.” Data such as those from Dr. Joseph’s study can also inform recommendations on timing of maternal vaccination.
“For instance, Dr. Joseph demonstrated that, 28 days out from the infection, you had more antibodies, so there may be a scenario where we say this vaccine may be more beneficial in the middle of the pregnancy for the purpose of forming those antibodies,” Dr. Louis said.
Consensus emerging from maternal antibodies data
The findings from Dr. Joseph’s study mirror those reported in a study published online Jan. 29 in JAMA Pediatrics. That study, led by Dustin D. Flannery, DO, MSCE, of Children’s Hospital of Philadelphia, also examined maternal and neonatal levels of IgG and IgM antibodies against the receptor binding domain of the SARS-CoV-2 spike protein. They also found a positive correlation between cord blood and maternal IgG concentrations (P < .001), but notably, the ratio of cord to maternal blood titers was greater than 1, unlike in Dr. Joseph’s study.
For their study, Dr. Flannery and colleagues obtained maternal and cord blood sera at the time of delivery from 1471 pairs of mothers and infants, independently of COVID status during pregnancy. The average maternal age was 32 years, and just over a quarter of the population (26%) were Black, non-Hispanic women. About half (51%) were White, 12% were Hispanic, and 7% were Asian.
About 6% of the women had either IgG or IgM antibodies at delivery, and 87% of infants born to those mothers had measurable IgG in their cord blood. No infants had IgM antibodies. As with the study presented at SMFM, the mothers’ infections included asymptomatic, mild, moderate, and severe cases, and the degree of severity of cases had no apparent effect on infant antibody concentrations. Most of the women who tested positive for COVID-19 (60%) were asymptomatic.
Among the 11 mothers who had antibodies but whose infants’ cord blood did not, 5 had only IgM antibodies, and 6 had significantly lower IgG concentrations than those seen in the other mothers.
In a commentary about the JAMA Pediatrics study, Flor Munoz, MD, of the Baylor College of Medicine, Houston, suggested that the findings are grounds for optimism about a maternal vaccination strategy to protect infants from COVID-19.
“However, the timing of maternal vaccination to protect the infant, as opposed to the mother alone, would necessitate an adequate interval from vaccination to delivery (of at least 4 weeks), while vaccination early in gestation and even late in the third trimester could still be protective for the mother,” Dr. Munoz wrote.
Given the interval between two-dose vaccination regimens and the fact that transplacental transfer begins at about the 17th week of gestation, “maternal vaccination starting in the early second trimester of gestation might be optimal to achieve the highest levels of antibodies in the newborn,” Dr. Munoz wrote. But questions remain, such as how effective the neonatal antibodies would be in protecting against COVID-19 and how long they last after birth.
No external funding was used in Dr. Joseph’s study. Dr. Joseph and Dr. Louis have disclosed no relevant financial relationships. The JAMA Pediatrics study was funded by the Children’s Hospital of Philadelphia. One coauthor received consultancy fees from Sanofi Pasteur, Lumen, Novavax, and Merck unrelated to the study. Dr. Munoz served on the data and safety monitoring boards of Moderna, Pfizer, Virometix, and Meissa Vaccines and has received grants from Novavax Research and Gilead Research.
A version of this article first appeared on Medscape.com.