COVID-19 mRNA vaccines in pregnancy led to strong immune responses for mothers, infants

Key takeaways:

• COVID-19 vaccination led to strong immune response — highest for those vaccinated in the second trimester.
• Vaccination in second and third trimesters led to positive immune response up to 6 months for infants.

COVID-19 messenger RNA vaccination during pregnancy resulted in a robust immune response without adverse outcomes for both mothers and infants for almost 6 months after birth, according to a cohort study published in JAMA Network Open.

“Pregnant individuals may worry about the theoretical risks of vaccine adverse effects, especially fever, on the developing fetus. Conversely, lack of symptoms may lead a vaccine recipient to question whether the vaccine is working,” Arianna G. Cassidy, MD, division of maternal-fetal medicine in the department of obstetrics, gynecology and reproductive sciences at the University of California, San Francisco, and colleagues wrote. “Although passively transferred antibodies after maternal vaccination have been shown to protect the infant against COVID-19 for up to 6 months of life, there are few data on longitudinal, linked outcomes for mother-infant dyads from pregnancy through the first year of life.”

Cassidy and colleagues conducted a prospective cohort study with 76 pregnant women (median age, 35 years; 67.1% white) who were also enrolled in the COVID-19 Vaccination in Pregnancy and Lactation study from December 2020 to December 2021. All pregnant women received at least two doses of the mRNA-1273 (Moderna; n = 34) or the BNT162b2 (Pfizer-BioNTech; n = 42) messenger RNA (mRNA) COVID-19 vaccine during pregnancy, and most received a third dose after delivery.

The primary outcomes were vaccine response measured by blood immunoglobulin G (IgG) titers after each dose and self-reported symptoms after vaccination. Mother and infant blood and breastmilk were sampled for up to 1 year after delivery for IgG and IgA titers.

After the second vaccine dose, systemic symptoms were more common compared with after the first dose (71.2% vs. 44.1%; P = .007). In addition, systemic symptoms were more common following the mRNA-1273 vaccine compared with BNT162b2 (92.6% vs. 53.1%; P = .001).

Systemic symptoms were linked to 65.6% higher median IgG titers compared with no symptoms after the second COVID-19 vaccine dose (median, 2,596 vs. 1,568 relative fluorescent units; P = .007). Mean cord titers among women with local or systemic symptoms were 6.3-fold higher compared with women without symptoms from the vaccine.

In all trimesters, receiving a COVID-19 vaccine resulted in a robust maternal IgG response; however, the IgG transfer ratio was highest among women who were vaccinated during their second trimester. Regardless of vaccination trimester, anti-SARS-CoV-2 IgG was still detectable in cord blood. Infants of women vaccinated in the second and third trimesters had positive IgG titers for at least 5 to 6 months after birth. In addition, IgG and IgA titers remained high in milk for at least 5 to 6 months after birth.

Researchers observed no adverse perinatal outcomes related to vaccination.

“Systemic symptoms after receipt of a vaccine dose may indicate a more robust immune response, as measured by higher antibody titers,” the researchers wrote. “The association between postvaccination symptoms and magnitude of immune response warrants further study.”