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• Posted November 28, 2023

COVID Vaccines Curbed Pandemic-Linked Surge in Preemie Births

COVID vaccines saved the lives and health of countless babies by preventing their premature births, a new study shows.

COVID-19 initially caused an alarming surge in premature birth rates, but those returned to pre-pandemic levels following the introduction of vaccines, researchers found.

These findings should help allay vaccine hesitancy among pregnant women, said researcher Jenna Nobles, a professor of sociology with the University of Wisconsin-Madison.

“The results here are compelling evidence that what will actually harm the fetus is not getting vaccinated. That's a message practitioners can share with concerned patients,” Nobles said in a university news release.

The COVID virus endangers pregnancies by causing inflammation and immune responses that can damage the placenta, among other potentially harmful effects, researchers explained in background notes.

For this study, Nobles and her colleagues analyzed California birth records for nearly 40 million people, from the early days of the pandemic through to the introduction of COVID vaccines.

Researchers found that as the virus spread between July and November 2020, the likelihood that a COVID-infected expecting mom in California would give birth more than three weeks before her due date was 5.4 percentage points higher than anticipated -- 12.3% instead of 6.9%.

But the excess risk of preterm birth fell slightly in early 2021 and then dropped steeply in 2022, researchers found. At that point, maternal COVID infection during pregnancy caused no excess risk of preterm birth.

By dividing up birth records geographically, researchers determined that vaccines contributed to that decrease.

“In ZIP codes with the highest vaccination rates, the excess risk of preterm birth declines much faster,” Nobles said. “By summer 2021, having COVID-19 in pregnancy had no effect on preterm birth risk in these communities. It takes almost a year longer for that to happen in the ZIP codes with the lowest vaccine uptake.”

“That highlights how protective COVID vaccines have been,” Nobles added. “By increasing immunity faster, early vaccination uptake likely prevented thousands of preterm births in the U.S.”

The findings were published Nov. 27 in the Proceedings of the National Academy of Sciences.

Preterm birth is a leading contributor to infant mortality, and it also is associated with a host of short- and long-term health problems for children. Being born even just a few weeks early reduces a child's expected educational attainment, health and savings as an adult, researchers noted.

“This is still an evolving epidemic, and the rate of vaccine boosters among pregnant people right now is very low,” Nobles said. “The question is, how many more iterations of viral evolution does this need to escape the immunity that we have? It's miraculous and incredible that we're now down to essentially zero additional preterm births, but it does not indicate that it's going to be that way in perpetuity.”

More information

The National Institutes of Health have more on how COVID-19 affects pregnancy.

SOURCE: University of Wisconsin-Madison, news release, Nov. 27, 2023