Infants and COVID Antibodies

Vaccination during pregnancy equals more persistent infant antibody levels

Photo of a hand with a stethoscope on a newborn baby's chest
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This article is part of Harvard Medical School’s continuing coverage of COVID-19.

With the COVID-19 pandemic entering its third year, efforts to mitigate the risk for infection remain vitally important, especially for vulnerable populations.

A recent study by Harvard Medical School scientists at Massachusetts General Hospital showed that vaccination during pregnancy resulted in more persistent antibody levels in infants, when compared with babies born to unvaccinated mothers infected with SARS-CoV-2. 

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The study, published in The Journal of the American Medical Association (JAMA), included individuals vaccinated with two doses of an mRNA vaccine or infected at 20 to 32 weeks’ gestation, when transfer of antibodies through the life-giving placenta has shown to be at its peak. 

Titers, or antibody levels, were higher in vaccinated mothers and their umbilical cord blood at delivery than in a study of participants infected with SARS-CoV-2.

After two months, 98 percent of the infants (48 of 49) born to vaccinated mothers had detectable levels of the protective immunoglobulin G (IgG), the most common antibody found in blood.

At six months, the researchers looked at 28 of the infants born to vaccinated mothers and found 57 percent (16 of 28) still had detectable IgG. That was compared with just 8 percent (1 of 12) born to infected mothers. 

“While it’s still unclear just how high the titer needs to be to completely protect an infant from COVID, we know antispike IgG levels correlate with protection from serious illness,” said co-senior author Andrea Edlow, HMS associate professor of obstetrics, gynecology and reproductive biology and maternal-fetal medicine specialist at Mass General and director of the Edlow Lab in the Vincent Center for Reproductive Biology.

“The durability of the antibody response here shows vaccination not only provides lasting protection for mothers but also antibodies that persist in a majority of infants to at least six months of age,” Edlow said.

“Many interested parties, from parents to pediatricians, want to know how long maternal antibodies persist in infants after vaccination, and now we can provide some answers. We hope these findings will provide further incentive for pregnant people to get vaccinated, especially with the emergence of new variants of concern like omicron,” she added.

The authors noted the limitations to their research, including the small study cohort, delays in follow-up with the infected group due to participants’ availability and COVID-19 surges in Boston, as well as reporting of titers as opposed to clinical outcomes. 

“Pregnant women are at extremely high risk for serious complications from COVID,” said Galit Alter, HMS professor of medicine, core member of the Ragon Institute of MGH, MIT and Harvard, and co-senior author of the study.

“And given the lag in development of COVID-19 vaccines for infants, these data should motivate mothers to get vaccinated and even boosted during pregnancy to empower their babies’ defenses against COVID,” Alter said.

Funding for the study included grants from the National Institute of Child Health and Human Development (NICHD), the March of Dimes, the Gates Foundation, and The National Institute of Allergy and Infectious Diseases (NIAID).

Adapted from a Mass General news release.