mRNA COVID-19 vaccines induced an antibody response in both mothers and babies for at least 6 months after birth, with no adverse outcomes, according to a single-center study published late last week in JAMA Network Open.
University of California researchers evaluated the medical records of 76 COVID-naïve mothers in San Francisco who received an mRNA vaccine during pregnancy from December 2020 to December 2021, with follow-up through March 2022.
Mothers gave blood samples before vaccination and after each dose and completed an online questionnaire about adverse effects 28 days after doses. The team also measured immunoglobulin G (IgG) concentrations in umbilical cord blood at delivery and in infant blood and IgG and immunoglobulin A (IgA) levels in breast milk four times for 1 year.
Average maternal age was 35 years, 67.1% were White, 55.3% received the Pfizer/BioNTech vaccine, 44.7% received the Moderna version, and the median gestational age at first dose was 22.8 weeks.
Systemic vaccine-related symptoms tied to higher IgG
Systemic vaccine-related symptoms were more common after the second vaccine dose than after the first (71.2% vs 44.1%) and after the Moderna than the Pfizer vaccine (92.6% vs 53.1%). Systemic symptoms were tied to 65.6% higher median IgG concentrations than no symptoms after dose two, and average cord levels in participants with symptoms were 6.3-fold higher than in those with no symptoms.
Systemic symptoms after receipt of a vaccine dose may indicate a more robust immune response.
While vaccination in all trimesters triggered a robust maternal IgG response, the IgG transfer ratio was highest among those vaccinated in the second trimester. IgG was also detected in cord blood in all trimesters. IgG and IgA concentrations in breast milk remained positive for at least 5 or 6 months after birth, and infants born to women vaccinated in the second and third trimesters had positive IgG levels over the same period. No vaccine-attributed adverse outcomes occurred.
"Systemic symptoms after receipt of a vaccine dose may indicate a more robust immune response, as measured by higher antibody titers," the study authors wrote. "The association between postvaccination symptoms and magnitude of immune response warrants further study."