COVID-19 Vaccines and Boosters Associated with Lower Rates of Stillbirth, New ISB Study Shows

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ISB Associate Professor Dr. Jennifer Hadlock, left, and Research Scientist Dr. Samantha Piekos.

Pregnant people who are vaccinated are less likely to contract COVID-19 than unvaccinated pregnant people, and those vaccinated and boosted are less likely to get COVID than those who are vaccinated only, according to the first-ever large study of COVID boosters in pregnant people. The study was led by the Institute for Systems Biology (ISB) in Seattle, and was published in Lancet Digital Health.

“We found that vaccinated pregnant people had lower COVID-19 rates than those who were unvaccinated, and that the pregnant people who were vaccinated and boosted had even lower rates,” said ISB Research Scientist Samantha Piekos, PhD, who led the study.

Piekos and colleagues also found that vaccinated people were less likely to have poor birth outcomes like preterm birth, stillbirth, or very low birth weight (below 3.3 pounds) compared to unvaccinated pregnant people. Those who were vaccinated and also had a booster were less likely to have stillbirth compared to those vaccinated without boosters, but there was no statistical difference with preterm birth or very low birth weight.

The research team examined the impact of COVID-19 vaccinations on maternal-fetal outcomes for nearly 92,000 people who delivered their babies in the Providence healthcare system between January of 2021 and October of 2022. The team examined electronic health records, and controlled for several confounding variables, including demographics, lifestyle, and other clinical, geographical and chronological factors that were disproportionately skewed between vaccinated and unvaccinated cohorts.

“The take-home message is COVID-19 vaccination is associated with better maternal-fetal outcomes, and boosters are associated with further reduced rates of stillbirth,” said Jennifer Hadlock, MD, corresponding author of the paper and an associate professor at ISB.

The findings have already made their way into the Providence system.

“I cite this data to my patients,” said Tanya Sorensen, MD, a specialist in maternal and fetal medicine at Providence Swedish in Seattle, and who is an author of the research paper. “Vaccines and boosters help keep mom and baby safe.”

As we move into the endemic phase of COVID-19, it remains important to remember that vaccinations and boosters are especially critical for pregnant people. This research builds on the authors’ previously published study that showed even mild cases of COVID-19 during pregnancy can increase risk for poor birth outcomes.