Cookies on this website

We use cookies to ensure that we give you the best experience on our website. If you click 'Accept all cookies' we'll assume that you are happy to receive all cookies and you won't see this message again. If you click 'Reject all non-essential cookies' only necessary cookies providing core functionality such as security, network management, and accessibility will be enabled. Click 'Find out more' for information on how to change your cookie settings.

BACKGROUND: In early 2023, when Omicron was the variant of concern, we showed that vaccinating pregnant women decreased the risk of severe COVID-19 related complications, and maternal morbidity and mortality. OBJECTIVES: To analyze the impact of COVID-19 during pregnancy on newborns and the effects of maternal COVID-19 vaccination on neonatal outcomes, when Omicron was the variant of concern. STUDY DESIGN: INTERCOVID-2022 is a large, prospective, observational study, conducted in 40 hospitals across 18 countries, from November 27, 2021 (the day after the World Health Organization declared Omicron the variant of concern) to June 30, 2022, to assess the effect of COVID-19 in pregnancy on maternal and neonatal outcomes, as well as vaccine effectiveness (VE). Women diagnosed with laboratory-confirmed COVID-19 in pregnancy were compared with two 'non-diagnosed', unmatched women recruited concomitantly and consecutively in pregnancy or at delivery. Mother/newborn dyads were followed until hospital discharge. Primary outcomes were a neonatal positive test for COVID-19, severe neonatal morbidity index (SNMI), severe perinatal morbidity and mortality index (SPMMI), preterm birth, neonatal death, referral to neonatal intensive care unit (NICU), and diseases during the neonatal period. VE was estimated adjusted by maternal risk profile. RESULTS: We enrolled 4707 neonates born to 1577 (33.5%) mothers diagnosed with COVID-19 and 3130 (66.5%) non-diagnosed mothers. Amongst diagnosed mothers, 642 (40.7%) were not vaccinated, 147 (9.3%) were partially vaccinated, 551 (34.9%) were completely vaccinated, and 237 (15.0%) also had a booster vaccine. Neonates of booster-vaccinated mothers had less than half (RR=0.46; 95%CI=0.23, 0.91) the risk of being diagnosed with COVID-19 compared to those of unvaccinated mothers; they also had the lowest rates of preterm birth, medically-indicated preterm birth, respiratory distress syndrome and number of days in NICU. Newborns of unvaccinated mothers had double the risk of neonatal death (RR=2.06; 95% CI=1.06, 4.00) compared to those of non-diagnosed mothers. Vaccination was not associated with any congenital malformations. Although all vaccines provided protection against neonatal test positivity, newborns of booster-vaccinated mothers had the significantly highest VE (64%; 95% CI=10-86%); VE was not as high for mRNA vaccines only. VE against moderate/severe neonatal outcomes was much lower: 13% in the booster-vaccinated group (all vaccines), and 25% and 28% in the completely and booster-vaccinated groups, respectively (mRNA vaccines only). Vaccines were fairly effective in protecting neonates when given to pregnant women 100 days (14 weeks) or less before birth; thereafter, the risk increased and was much higher after 200 days (29 weeks).. Finally, none of the neonatal practices studied, including skin-to-skin contact and direct breastfeeding, increased the risk of infecting newborns. CONCLUSION: When Omicron was the variant of concern, newborns of unvaccinated mothers had an increased risk of neonatal death. Neonates of vaccinated mothers had a decreased risk of preterm birth and adverse neonatal outcomes. As the protective effect of COVID-19 vaccination decreases with time, to ensure that newborns are maximally protected against COVID-19 mothers should receive a vaccine or booster dose no more than 14 weeks before the expected date of delivery.

Original publication




Journal article


Am J Obstet Gynecol

Publication Date



COVID-19, COVID-19 vaccination, SARS-CoV-2, SARS-CoV-2 exposure, morbidity, mortality, multicenter study, neonatal health, neonatal intensive care admission, neonatal outcomes, neurologic outcomes, newborn, perinatal practices, pregnancy, preterm birth, respiratory support, respiratory symptoms, skin-to-skin