Fewer pregnant women had severe COVID-19 in the Omicron variant-era than during periods dominated by previous strains, and vaccinated patients were better protected than their unvaccinated peers, according to research published yesterday in the American Journal of Infection Control.
Investigators from South Korea retrospectively examined the electronic medical records of 224 pregnant women who tested positive for COVID-19 and 82 quarantine deliveries from Nov 1, 2020, to Mar 7, 2022, at a single hospital. Average maternal age was 32 years.
Pregnant women admitted to the hospital before Jan 17, 2022 were considered to be infected with the Delta variant, while those after that date were considered infected with Omicron. Of the 224 women, 39 (17%) were vaccinated, and 185 (83%) were unvaccinated against COVID-19.
Most women in both the Delta and Omicron periods were in their third semester (53.1% and 73.4%, respectively), but the authors said the high percentages could be because many were admitted for delivery.
The authors noted that the number of pregnant women infected with COVID-19 and having cesarean deliveries has risen steadily throughout the pandemic in South Korea. The COVID-19 vaccination rate in pregnant women in that country is low, at 9.8%.
Relative influence of Omicron, vaccination unknown
Of the 224 women, 42% tested positive for COVID-19 amid Omicron, and 4.1% of vaccinated women and 25% of their unvaccinated counterparts in this period had severe illness. A total of 2.6% and 16.2%, respectively, required supplemental oxygen.
Rates of moderate or severe maternal illness fell from 30.0% amid Delta to 10.6% amid Omicron, as did rates of infection (27.7% to 13.8%). The need for supplemental oxygen also dropped from 20.0% to 5.3%.
Before Omicron, 6.9% of the patients were vaccinated against COVID-19, rising to 31.9% after its emergence. Rates of moderate or severe illness were significantly lower in the vaccinated group than in the unvaccinated group (25.4% vs 4.1%), as was the need for extra oxygen (16.2% vs 2.6%). Only one vaccinated patient, who had asthma, needed oxygen therapy.
"Overall, patients had a more favorable clinical course in the omicron era," the authors wrote. "Moreover, vaccinated patients were better protected than non-vaccinated patients, indicating the importance of vaccination against COVID-19."
But the researchers acknowledged that they couldn't determine whether the reduced COVID-19 severity in vaccinated pregnant women was caused by the vaccination, or was due to characteristics of Omicron. "Further studies are required to identify whether the outcomes improved due to the decreased severity of the disease caused by the omicron variant or the protective effects of vaccination," they concluded.