(NewsNation) — New research finds that infants born to mothers who were infected with COVID-19 during pregnancy have three times the risk of developing respiratory distress compared to unexposed infants.

The study published Wednesday in the journal Nature Communications indicates the risk was significantly lower when mothers were previously vaccinated. It adds to growing evidence that COVID vaccines are safe and effective for pregnant women.

“Researchers found that in-utero exposure to SARS-CoV-2 sparked an ‘inflammatory cascade’ in the infants, increasing the risk of a breathing disorder that most often strikes prematurely born infants,” UCLA Health said in a news release.

Respiratory distress occurs in babies whose lungs are not fully developed, according to Nationwide Children’s Hospital. Signs and symptoms include rapid and difficult breathing and changes in colors of the lips, fingers and toes.

A total of 221 mothers were enrolled in the study, producing 199 babies (some did not follow up and some were lost to miscarriage or other fetal demise). A total of 151 (68%) mothers were unvaccinated prior to infection.

Researchers found 17% of the exposed babies exposed to COVID in the womb had respiratory distress, a rate three times higher than seen in the general, unexposed population where only about 5% to 6% of newborns get respiratory distress.

Of the 34 infants with respiratory distress, only 5 (16%) were born to mothers vaccinated prior to infection.

“Not only do our results show higher rates of (respiratory distress) in (exposed) infants when compared to the general population,” the researchers wrote, “but we observed more cases of (respiratory distress) at later gestational ages than anticipated, when neonates should presumably have more mature lung anatomy.”

More research is emerging about the long-term impacts of COVID and its vaccine, including a study published Monday finding no link between the vaccine and childhood developmental delay among infants born to mothers who had been vaccinated.