Timing, number of COVID shots affect newborn protection

Mothers who want their newborns to have the highest levels of antibodies should receive their last vaccine dose during pregnancy.  And they should receive more than the baseline two vaccinations against the disease, according to a study published today in JAMA Network Open.

Even babies born prematurely can benefit from the maternal COVID-19 vaccines, the findings showed.

The UW Medicine-led study examined the maternal and umbilical cord blood in 220 pregnancies involving Seattle-area individuals who had never tested positive for COVID-19. The researchers compared the antibodies in the samples, noting the date of the participants’ most recent COVID-19 vaccination and the total COVID shots each mother had received before the baby’s delivery.  Participants gave birth at UW Medicine hospitals between Feb. 1, 2021, and Jan. 31, 2023.

Researchers found that the pregnant individuals who had three or more COVID-19 vaccine shots, including those who had the last shot closer to their delivery date, had about 10 times the amount of vaccine-specific antibodies in their blood and the baby’s cord blood at birth.

When the COVID-19 vaccine is administered during pregnancy, the antibodies the mother makes in response to the vaccine are transferred through the placenta to the fetus, the paper noted.

“In the absence of a prior COVID-19 infection, having three or more shots seems to improve the maternal antibody concentrations within the baby,” said Dr. Alisa Kachikis, a UW Medicine maternal-fetal medicine specialist and the study’s lead author. “The other takeaway is that even if it’s a preterm birth, having more doses and having those doses closer to the birth date will increase antibody concentrations.”

Kachikis suggested that the best protection is afforded to prospective mothers who receive more than two COVID-19 vaccinations and who receive their most recent dose during pregnancy.

“There was no difference in the concentration of antibodies between babies who were born preterm and term, if you control for how many vaccine doses the pregnant persons received and the timing of vaccines prior for delivery,” Kachikis noted.

In all, 36 mothers delivered preterm (median gestation of 35 weeks) and 184 delivered at full term (39 weeks). The study participants’ average age was 34 years.  Before delivery, 121 of the participants received two doses of the COVID-19 vaccine and 99 received three or more doses.

The authors noted that, while much research to date has focused on the importance of getting vaccinated against COVID-19 during pregnancy, few studies have looked at the presence of antibodies when comparing preterm and term births, or at the impact of the number or timing of shots.  

The study was supported by a grant from the National Institute of Allergies and Infectious Diseases (K23 A1153390).  

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