Maternal COVID-19 vaccination lowers risks for preterm birth, adverse outcomes

Key takeaways:

• Infants born to vaccinated vs. unvaccinated mothers had a lower risk for COVID-19.
• Respiratory distress syndrome rates and NICU days were lower for infants born to vaccinated vs. unvaccinated mothers.

Infants born to mothers vaccinated against COVID-19 during the omicron wave had decreased risks for preterm birth and adverse neonatal outcomes, according to results of the INTERCOVID-2022 study.

Healio previously reported on results of the INTERCOVID-2022 study, wherein unvaccinated pregnant women with COVID-19 had a greater risks for severe symptoms, referral to a higher level of care, ICU admission and mortality compared with vaccinated counterparts.

“A Norwegian nationwide registry-based cohort study found that infants whose mothers received an mRNA vaccine had a substantially lower risk of testing positive for SARS-CoV-2 during the first 4 months of life compared with infants of unvaccinated mothers. This reduction was noted during the periods when the delta and omicron variants were predominant, although vaccine effectiveness seemed greater when delta predominated,” Fernando C. Barros, PhD, from the Post Graduate Program in Health in the Life Cycle at the Catholic University of Pelotas, Brazil, and colleagues wrote. “The possible protective effect of vaccination on the risk of other adverse neonatal outcomes was not evaluated.”

INTERCOVID-2022, a prospective, observational cohort study, was conducted at 40 hospitals across 18 countries from November 2021 to June 2022. Researchers assessed effects of COVID-19 in pregnancy on maternal and neonatal outcomes and vaccine effectiveness during the omicron wave for 4,618 mothers and their 4,707 infants. All women delivered from September 2021 to June 2022. Each pregnant woman with a COVID-19 diagnosis in pregnancy was compared with two nondiagnosed counterparts.

Primary outcomes were a positive neonatal COVID-19 test, neonatal mortality, preterm birth, NICU referral and diseases during the neonatal period.

Overall, 33.5% of mothers were diagnosed with COVID-19, of whom 40.7% were not vaccinated, 9.3% were partially vaccinated, 34.9% were completely vaccinated and 15% were completely vaccinated and had a booster vaccine.

Results, published in the American Journal of Obstetrics & Gynecology, demonstrated that infants born to booster-vaccinated vs. unvaccinated mothers had lower COVID-19 diagnosis risk (RR = 0.46; 95% CI, 0.23-0.91). Vaccination effectiveness was greater for infants born to mothers with COVID-19 compared with infants born to mothers without (RR = 0.36; 95% CI, 0.14-0.9). Infants born to booster-vaccinated mothers were less likely to be born preterm (RR = 0.6; 95% CI, 0.39-0.93) and have a medically indicated preterm birth (RR = 0.46; 95% CI, 0.26-0.84) compared with infants born to unvaccinated mothers. Infants born to unvaccinated mothers had greater risks for infections (RR = 1.52; 95% CI, 1.16-1.98), antibiotic treatment (RR = 1.47; 95% CI, 1.09-1.97), respiratory support for more than 48 hours (RR = 1.65; 95% CI, 1.11-2.47) and neonatal death (RR = 2.06; 95% CI, 1.06-4) compared with infants born to booster-vaccinated mothers.

Vaccine effectiveness was 64% for infants born to booster-vaccinated mothers. Vaccine effectiveness against moderate to severe neonatal outcomes was 13% for booster-vaccinated mothers for all COVID-19 vaccines, and vaccine effectiveness was 25% for completely mRNA vaccinated mothers and 28% for mRNA booster-vaccinated mothers.

COVID-19 vaccinations were effective in protecting infants when administered 14 weeks or less before delivery, but risk increased when vaccines were administered 29 weeks before delivery.

According to the researchers, skin-to-skin contact and direct breastfeeding did not increase the risk for COVID-19 infection in infants.

“Unvaccinated mothers have newborn infants that are twice as likely to die in the neonatal period as those of vaccinated mothers,” the researchers wrote. “However, the protective effects of maternal vaccination diminish with time; hence, pregnant women should receive a vaccine or booster dose no more than 14 weeks before the expected date of delivery.”