COVID Vaccine Prevented Thousands of Premature Births in Pandemic—Study

COVID-19 infection during pregnancy increases a child's risk of being born prematurely, a new study has found. But this impact disappears after maternal vaccination, suggesting that the vaccine may have prevented thousands of premature births.

"Preterm birth is the leading cause of infant mortality in the United States, and it predicts worse health in childhood and adulthood as well as educational and economic setbacks later in life," study co-author Florencia Torche, a sociology professor at Stanford University, told Newsweek. "Very preterm birth, before 32 weeks of gestation, can have serious developmental consequences for children."

In their study, published in the Proceedings of the National Academy of Sciences, Torche and Jenna Nobles from the University of Wisconsin-Madison analyzed birth records from siblings born in California between 2014 and 2023. By comparing sibling births, the researchers found that from July to November 2020 mothers were nearly twice as likely to give birth three weeks before their due date.

"The increased risk of preterm birth occurred only for people with confirmed COVID-19 giving birth in hospitals in which all patients were tested at admission," Torche said.

"[Also] because we compare siblings, we are assessing the increased risk of preterm birth when someone has COVID-19 relative to that same mother's risk at their earlier births when they did not have COVID. We also statistically adjust for many factors that changed in people's lives between births, such as the mother's age, socioeconomic advantage and birth parity."

She continued: "Any alternative explanation for the patterns here would have to be something that caused a change in risk of preterm birth for someone from one birth to the next and was highly correlated with COVID-19 infection risk, [was] not measured in our study and...differentially changed in communities with higher vaccine uptake exactly at the time vaccines were rolled out. It's exceedingly difficult to come up with such alternative explanation."

But how exactly does a virus affect preterm births?

"COVID infection during pregnancy is associated with adverse health outcomes of both mothers and newborns," Torche said. "COVID-19 affects multiple biological systems, and there are likely several processes in play. We know that infections trigger immune and inflammation responses, and we have evidence now that COVID-19 can cause disintegration of the placenta. These, among other processes, can lead to preterm birth.

"Pregnant persons infected with COVID also have a higher risk of preeclampsia, ICU hospitalization and death. Their babies are more likely to be born preterm and to need intensive care," she said.

However, this sudden spike in preterm births began to dwindle in 2021, before disappearing almost entirely in 2022. The team traced this decrease in line with the rapid uptake of COVID-19 vaccinations across the U.S.

"Strikingly, the adverse impact of COVID-19 infection during pregnancy on preterm birth disappeared almost one year earlier in communities with high vaccination rates, compared to communities with low vaccination rates," Torche said. "This suggests vaccines might have prevented thousands of preterm births in the U.S."

Torche and Nobles believe that their results offer compelling evidence for the benefits of vaccination during pregnancy.

"All of the evidence we have produced indicates that COVID-19 vaccines are safe and highly effective in pregnancy," Torche said.

She went on: "One important factor accounting for vaccine hesitance is the concern among pregnant persons about vaccines' safety for the fetus. Our findings suggest that what will actually be harmful for the fetus is not receiving a vaccine. This is useful information that could be shared by health care providers with pregnant patients and people intending pregnancy."