In a prospective cohort study published in the Journal of the American Medical Association Network, researchers sought to investigate correlations between reactogenicity and immunogenicity of COVID-19 mRNA vaccination in each trimester of pregnancy, as well as antibody durability and clinical outcomes of mother-infant dyads until 1 year after birth.

This study included pregnant females enrolled in the COVID-19 Vaccination in Pregnancy and Lactation study from December 1, 2020, through December 31, 2021. Follow-up through March 31, 2022, was conducted at a large academic medical center in an urban metropolitan area in California. Pregnant females receiving COVID-19 mRNA vaccines were eligible. Of 81 enrolled participants, five were excluded after enrollment: one terminated pregnancy, one received the third vaccine dose before delivery, and three delivered before completing the initial vaccine series.

The primary outcomes were vaccine response as assessed by blood immunoglobulin G (IgG) titers after each vaccine dose and self-reported postvaccination symptoms. The patients’ IgG titers were measured in cord blood and in infant blood at intervals up to age 1 year; IgG and IgA titers were measured in maternal milk. Clinical outcomes were gathered from medical records.

The results revealed that in this cohort study of 76 females who received mRNA COVID-19 vaccines in pregnancy, systemic symptoms after vaccination were associated with 90% higher IgG titers after the second dose, and symptoms were associated with 6.3-fold higher cord blood IgG titers than in individuals without symptoms and there were no adverse outcomes. Additionally, offspring had positive IgG titers for at least 5 to 6 months.

The results also indicated that systemic symptoms were more common after receipt of the second vaccine dose than after the first dose, and systemic symptoms were associated with 65.6% higher median IgG titers than no symptoms after the second vaccine dose. Vaccination in all trimesters provoked a strong maternal IgG response, and the IgG transfer ratio was greatest among individuals vaccinated in the second trimester.

The authors noted, “These results suggest that mRNA COVID-19 vaccines in pregnancy provoke an IgG response for the mother-infant dyad for 6 months after birth and that systemic symptoms after vaccination may indicate a more robust immune response, without adverse outcomes.”

In conclusion, the authors wrote, “The findings of this cohort study indicated that vaccination with mRNA COVID-19 vaccines in pregnancy provoked a robust immune response for the mother-infant dyad for approximately 6 months after birth. Systemic symptoms after receipt of a vaccine dose may indicate a more robust immune response, as measured by higher antibody titers. The association between postvaccination symptoms and magnitude of immune response warrants further study.”

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