Science Update: Preterm infants protected by maternal COVID-19 vaccination, NIH-funded study suggests

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Preterm infants born to people who have been vaccinated for COVID-19 had roughly the same levels of antibodies to the spike protein of SARS-CoV-2 as term infants born to vaccinated people, according to a study funded by the National Institutes of Health (NIH). Moreover, in all infants, antibodies to the spike protein were higher among those born to individuals who had received three or more vaccine doses before delivery, compared to those who had only two prior vaccine doses. The findings may help allay concerns that fewer antibodies might pass to preterm infants than term infants.

The study was conducted by Alisa Kachikis, M.D., M.S., of the University of Washington, and colleagues. It appears in JAMA Network Open. NIH funding was provided by the Eunice Kennedy Shriver National Institute of Child Health and Human Development, the Office of Research on Women’s Health, the National Institute of Allergy and Infectious Diseases, and the National Center for Advancing Translational Sciences.


Pregnant individuals who are vaccinated against COVID-19 have lower rates of severe COVID-19 illness and pregnancy complications than unvaccinated pregnant people. COVID-19 vaccines protect against the disease by stimulating production of antibodies to the spike protein, which SARS-CoV-2 uses to infect cells. Previous research has shown that anti-spike antibodies pass from pregnant individuals through the placenta to the fetus and may protect infants from severe COVID-19 illness. However, little is known about how well anti-spike antibodies are transferred to preterm infants.


For the current study, researchers compared levels of anti-spike antibodies in 1) the blood of pregnant individuals with no history of COVID-19 infection who received mRNA vaccines and then gave birth and 2) the umbilical cord blood of these infants, who were born at term and preterm. The team also compared anti-spike antibody levels from those who had been vaccinated twice before delivery (including before pregnancy) and those who were vaccinated three or more times before delivery.

Of the 220 participants, 184 delivered full-term infants and 36 delivered preterm, while 121 had been vaccinated twice and 99 had been vaccinated three or more times. For those receiving 2 vaccine doses, the average concentration of anti-spike antibodies was 674. The average concentration was 8,159 among those who received 3 or more doses. For cord blood samples, the average was 1,000 after 2 doses and 9,992 after 3 or more doses. The researchers did not find a significant difference in umbilical cord antibody levels between infants delivered at term and preterm.


The findings provide assurance that preterm infants receive similar levels of maternal antibody protection as term infants after maternal COVID-19 vaccination. In addition, compared to receiving two doses of a vaccine, receiving 3 or more doses resulted in 10 times the level of anti-spike antibodies in umbilical cord blood. The authors concluded that policies should be considered for the administration and timing of COVID-19 vaccines for those at risk of preterm delivery.

Next Steps

Given that the two-dose vaccine series is no longer available and the current recommendation is for a single vaccine dose, additional research is needed to determine the ideal number of doses for pregnant individuals with and without a history of COVID-19 infection.


Kachikis, A, et al. Timing of maternal COVID-19 vaccine and antibody concentrations in infants born preterm. JAMA Network Open. 2024.

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