Pregnant women vaccinated against COVID-19 pass antibodies to newborns

Pregnant and lactating women who received the Pfizer/BioNTech or Moderna COVID-19 vaccine had similar levels of vaccine-induced antibody titers compared with nonpregnant controls, according to new study results.

In addition, researchers found vaccine-generated antibodies in umbilical cord blood and breast milk after maternal vaccination. The new findings suggest that COVID-19 vaccination in pregnant and lactating women can provide “robust maternal and neonatal immunity,” they wrote.

“This news of excellent vaccine efficacy is very encouraging for pregnant and breastfeeding women, who were left out of the initial COVID-19 vaccine trials” Andrea Edlow, MD, MSc, a maternal-fetal medicine specialist at Massachusetts General Hospital, said in a press release.

In the study, Edlow, Kathryn Gray, MD, PhD, an obstetrician at Brigham and Women’s Hospital, and colleagues assessed the immunogenicity and reactogenicity of COVID-19 vaccination with the Moderna and Pfizer/BioNTech vaccines in 131 women who were pregnant (n = 84), lactating (n = 31) and not pregnant (n = 16). All participants were aged between 18 and 45 years, most were white, about half received the Pfizer/BioNTech vaccine and five had a previous SARS-CoV-2 infection.

The pregnant women had a mean gestational age of 23.2 weeks when they received their first vaccine dose. Thirteen of them delivered during the study, and 10 provided cord blood at delivery. Among those with cord blood samples, nine received both COVID-19 vaccine doses.

Gray and colleagues wrote in the American Journal of Obstetrics and Gynecology that vaccine-induced antibody titer levels were comparable among all three cohorts, with a median interquartile range of 5.59 (95% CI, 4.68-5.89) in pregnant women, 5.74 (95% CI, 5.06-6.22) in lactating women, and 5.62 (95% CI, 4.77-5.98) in nonpregnant women.

The researchers compared antibody titer levels of vaccinated women in the current study with a separate cohort of 37 pregnant women who were infected with SARS-CoV-2 during pregnancy. They found “strikingly higher levels” of antibodies in pregnant women who were vaccinated than those who were infected with SARS-CoV-2 during pregnancy (P < .0001).

Vaccine-generated antibodies were found in all breast milk and umbilical cord blood specimens, the researchers reported. The woman’s second vaccine dose increased SARS-CoV-2-specific IgG in breast milk and maternal blood, they added. The cord blood sample with the lowest IgG response was from the one participant who only received one COVID-19 vaccine dose during pregnancy, “suggesting that two doses may be essential to optimize humoral immune transfer to the neonate,” the researchers wrote.

“Based on what is known about other vaccines, the amount of maternal IgG transferred across the placenta to the cord is likely to differ by trimester of vaccination,” Gray and colleagues wrote. “Understanding vaccine-induced antibody transfer kinetics across all pregnancy trimesters will be an important direction for future research. While timing maternal COVID-19 vaccination may not be possible during this phase of the pandemic, understanding optimal timing of vaccination to augment neonatal humoral immunity remains important.”

The study also showed that mucosal IgA responses were higher with the Moderna vaccine compared with the Pfizer/BioNTech vaccine, according to the researchers.

“This finding is important for all individuals, since SARS-CoV-2 is acquired through mucosal surfaces like the nose, mouth and eyes,” Gray said in the press release. “But it also holds special importance for pregnant and lactating women because IgA is a key antibody present in breast milk.”