“Vaccination coverage among pregnant women remains a priority,” the researchers wrote.
COVID-19 during the first 6 months of pregnancy, with the Omicron variant specifically, was found to increase the risk of maternal morbidity and severe complications among symptomatic, unvaccinated women, according to a paper published in The Lancet.1
“As it is very difficult to predict who is going to develop severe symptoms and complications with the exception of overweight women or women with obesity, universal vaccination is key during pregnancy,” the study authors wrote.
A team of investigators from the United Kingdom, the United States, Pakistan, Argentina, and other countries enrolled 4,618 pregnant women in a prospective, observational study in order to understand the maternal and perinatal outcomes of COVID-19 during pregnancy as well as vaccine effectiveness against the omicron variant.
The women were recruited from 41 hospitals across 18 countries, the study authors explained. These hospitals, they noted, are part of a “worldwide network of research institutions that provide routine care to several thousand women and newborn babies every year.” They also acknowledged that these hospitals were not selected to represent underlying populations, but instead to allow the investigators to enroll the maximum number of diagnosed and non-diagnosed women in the shortest possible timeframe.
The study authors matched each woman with laboratory-confirmed COVID-19 with 2 unmatched women without a COVID-19 diagnosis. These women were enrolled from the day after the World Health Organization declared omicron a variant of concern, Nov. 27, 2021, and June 30, 2022. The investigators included live and stillborn singleton and multiple births, as well as newborns with congenital abnormalities, they said. They were included in follow-up data until the time of hospital discharge.
A third of the women enrolled (1,545 women) had COVID-19 diagnosis from 36.7 weeks, while the remaining two-thirds did not have a COVID-19 diagnosis, the study authors said. Despite similar demographic characteristics, the study authors noted smokers among the 2 groups (8 percent among the COVID-19-diagnosed participants; 6 percent among the otherwise healthy participants), people who were overweight or with obesity (49 percent vs. 47 percent), and those who had slightly fewer pre-existing morbidities (18 percent vs. 20 percent).
The study authors determined that women with a COVID-19 diagnosis had an increased risk for maternal morbidity and mortality index (MMMI) and severe perinatal morbidity and mortality index (SPMMI) compared to their non-COVID-19-diagnosed counterparts. Additionally, this group had an increased risk for severe neonatal morbidity index (SNMI) but it was lower, the investigators reported.
In looking at the impact of vaccination, the study authors observed that unvaccinated women with COVID-19 diagnosis had a greater risk of MMMI. Additionally, severe cases of COVID-19 symptoms in unvaccinated women increased the risk of severe maternal complications, perinatal complications, and referral, ICU admission, or death, the study authors found.
A majority (63 percent) of the participants had at least a single dose of any COVID-19 vaccine, the study authors said, while about half (54 percent) had either complete or booster doses of the vaccine. The study authors determined that vaccine effectiveness – that is, all vaccines combined – for severe complications from COVID-19 for all women with a complete regimen was 48 percent, and 76 percent following a booster dose. Furthermore, for women with a COVID-19 diagnosis, vaccine effectiveness of all vaccines combined for participants with a complete regimen was 74 percent, and reached 91 percent following a booster dose, the study authors said.
“COVID-19 in pregnancy, during the first 6 months of omicron as the variant of concern, was associated with increased risk of severe maternal morbidity and mortality, especially among symptomatic and unvaccinated women,” the study authors concluded. “Women with complete or boosted vaccine doses had reduced risk for severe symptoms, complications, and death. Vaccination coverage among pregnant women remains a priority.”
1. Villar, J et al. Pregnancy outcomes and vaccine effectiveness during the period of omicron as the variant of concern, INTERCOVID-2022: a multinational, observational study. The Lancet. 2023. https://doi.org/10.1016/S0140-6736(22)02467-9