THURSDAY, Nov. 10, 2022 (HealthDay News) — Time from infection or vaccination to delivery is the most important factor in transfer efficiency of COVID-19 protection from mother to infant, according to a study published online Nov. 9 in JAMA Network Open.

Dustin D. Flannery, D.O., from the Children’s Hospital of Philadelphia, and colleagues examined whether placental antibody transfer after COVID-19 vaccination differs from after severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection in pregnant individuals. Maternal and cord blood serum samples were analyzed for antibody-level measurements for 585 maternal-neonatal dyads (Aug. 9, 2020, to April 25, 2021).

The researchers found that immunoglobulin (Ig) G was detected in cord blood from 95.2 percent of newborns. Among 169 vaccine recipients, the geometric mean IgG level was significantly higher versus 408 persons after infection (33.88 arbitrary U/mL versus 2.80 arbitrary U/mL). After vaccination with the mRNA-1273 (Moderna) vaccine, the geometric mean IgG levels were higher than for the BNT162b2 (Pfizer/BioNTech) vaccine (53.74 arbitrary U/mL versus 25.45 arbitrary U/mL). After vaccination, placental transfer ratios were lower versus after infection (0.80 versus 1.06) but were similar between the mRNA vaccines. Time from infection or vaccination to delivery was associated with transfer ratio when adjusting for gestational age at delivery and maternal hypertensive disorders, diabetes, and obesity. As early as 26 weeks of gestation, placental antibody transfer was detectable. Transfer ratio higher than 1.0 was seen among 94.1 percent of births at ≥36 weeks of gestation by eight weeks after vaccination.

“Given that pregnancy is a risk factor for severe COVID-19, this study suggests pregnant people should prioritize getting vaccinated to protect themselves and their babies,” Flannery said in a statement.

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