Full-term babies of mothers infected with COVID-19 during pregnancy had triple the risk of experiencing respiratory distress (RD) compared to those who weren't exposed to the virus before they were born, researchers from the University of California Los Angeles (UCLA) reported today.
Another key finding was that the risk of RD in babies was lower in mothers who had received at least one COVID vaccine dose.
The group also conducted another arm of the study to look for clues about why the babies exposed to the virus were more likely to have RD, even though they themselves weren't infected with the virus. They found inflammatory markers that suggest a hyperimmune response and some hints of impaired respiratory function. Their findings appear today in Nature Communications.
Respiratory problems also occurred later than expected
COVID-19 infection during pregnancy already comes with well-known risks of premature birth, stillbirth, and severe complications for pregnant women. Those threats have underscored recommendations that pregnant women receive the COVID vaccine to protect both themselves and their babies.
The study included 221 pregnant women with COVID and 227 exposed babies from the UCLA Medical Center system. The analysis included 199 infants born between April 2020 and August 2022. Most COVID infections occurred in winter 2020, when the ancestral SARS-CoV-2 strain circulated.
In total, 34 babies experienced RD after they were born. The most common diagnoses were respiratory distress syndrome, followed by transient tachypnea (abnormally rapid breathing) and other infections. No deaths were reported.
For comparison, the group noted that the overall incidence of RD in unexposed babies ranges from 5.2% to 6.4%. For the exposed infants in the study, the incidence of RD was unusually high, at 17%. The odds ratio of RD in babies born to unvaccinated mothers, compared to vaccinated moms, was 3.06 (95% confidence interval, 1.08 to 10.21).
Researchers also saw RD crop up at later gestational ages than usually seen—a time when newborns presumably have more mature lung development.
Of the 221 mothers, 68% were unvaccinated prior to their infection. Of unvaccinated moms, 16% had severe or critical disease, which was higher than the 4% in the vaccinated group. Of the babies with RD, 5 (16%) were born to vaccinated mothers, compared to 63 (41%) without the breathing disorder, suggesting a protective effect from the vaccine.
More clues on how RD develops after COVID exposure
For the second part of the study, the group conducted a proteomic study, which examines the structure and function of proteins and how they affect cells, to shed more light on the underlying causes of RD in exposed infants. They examined findings in 52 babies, which included 45 from the study group and 7 controls among infants born healthy after unexposed pregnancies.
They identified elevated levels of cytokines that had already been seen in exposed infants who developed RD, along with five unique findings. Their experiments found that 36 proteins were differentially expressed in exposed preterm babies with RD.
Also, they found that motile cilia—whiplike structures that help clear mucus from the respiratory tract—didn't function normally in exposed infants who developed RD.
Clear vaccine benefits, with a few data caveats
The group pointed out a few limitations of the study, including that the mothers and their babies were recruited from a large medical center that typically handles the sickest patients, which they said could skew the findings toward more severe illness than found in the general population.
They also pointed out that they weren't able to gauge the impact of COVID infection before and after vaccination, factors that could influence severity of maternal infection and fetal development.
Researchers also urged caution in interpreting the results due to small sample size.
Still, they note that one of the main messages of the findings was the vaccine's positive impact. "Pregnant persons should be encouraged to receive mRNA COVID-19 vaccines, regardless of history of prior COVID-19 infection," they wrote, adding that more research is needed to more fully understand the impact of COVID vaccination on long-term infant health, including chronic lung conditions.
