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For pregnant people, three doses of an mRNA COVID-19 vaccine resulted in 10-fold higher antibody levels in umbilical cord samples of preterm and full-term deliveries compared with only two doses, a prospective cohort study showed.

Geometric mean concentration of cord SARS-CoV-2 anti-Spike (anti-S) antibodies increased from 1,000 after two doses of vaccine to 9,992 for those who received three or more doses (P<0.001), reported Alisa Kachikis, MD, of the University of Washington in Seattle, and colleagues in .

In addition, concentrations of SARS-CoV-2 anti-S antibodies in paired maternal blood samples significantly increased, from 674 in those who received two vaccine doses to 8,159 in those who received 3 or more doses (P<0.001).

Notably, cord anti-S antibody levels were similar in preterm and full-term pregnancies, with geometric mean concentrations of 8,818 and 10,423, respectively (P=0.34). After adjusting for vaccine timing and dose number before delivery, there was no association between preterm delivery and cord anti-S antibody levels (β=0.44, 95% CI -0.06 to 0.94).

"We were surprised that, when adjusted for vaccine dose number and time from last vaccine dose, preterm babies received similar benefit from COVID-19 vaccines given to their mothers compared to term babies," Kachikis told 番茄社区app. "It shows that maternal antibody concentrations matter and we should consider high-risk pregnancies when thinking about timing of vaccines during pregnancy."

For both preterm and full-term pregnancies, the median time between last vaccine dose and delivery was 16 weeks, and the median gestational age at last vaccine dose was 25 weeks.

"Changes in antibody levels didn't really seem to correlate much with gestational age at the time of birth, so we shouldn't necessarily time a booster injection to the last few weeks of pregnancy thinking that's going to be most protective for the newborn," Angela Bianco, MD, director of maternal-fetal medicine at the Icahn School of Medicine at Mount Sinai in New York City, told MedPage Today. "We probably should encourage women even earlier in pregnancy or at the outset of pregnancy to get boosted if they haven't already."

A study from October showed that maternal mRNA COVID-19 vaccination during pregnancy protected young infants from COVID-related hospitalization, and another study found that maternal vaccination lowered risks of poor neonatal outcomes. However, a showed that although 58.7% of pregnant women had completed the primary COVID vaccination series, only 27.3% reported receiving an updated booster dose before or during their current pregnancy.

The current study enrolled 220 pregnant individuals at the University of Washington from February 2021 through January 2023. All had received at least two doses of mRNA COVID vaccine before giving birth and had no history of prior COVID infection (confirmed by the absence of anti-SARS-CoV-2 nucleocapsid antibodies at delivery). The median age of participants was 34 years, and approximately 82% were white.

Among participants, 121 received two doses of an mRNA vaccine and 99 received three or more vaccine doses, before or during pregnancy. Of the 36 preterm deliveries, the median gestational age was 35.1 weeks, but ranged from approximately 28 to 37 weeks, including 19.4% delivered at less than 34 weeks. The 184 full-term infants were delivered at a median 39.5 weeks. Cesarean section delivery was more common among preterm infants than those carried to full term (66.7% vs 35%, respectively).

Kachikis and colleagues noted that the study was limited by its small sample size. Because selection criteria required participants to have received at least two doses of an mRNA vaccine, the study population was limited to those with high vaccine acceptance rates.

Bianco also noted that the study population was mostly white individuals with private health insurance who had never had COVID. Additionally, very few early preterm deliveries were included and the researchers did not specify the causes of preterm deliveries. These factors mean the findings of the study might not apply to other populations, she explained.

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