Vaccine Effectiveness in SARS-CoV-2-Infected Pregnant Women with Gestational Diabetes Mellitus: Results from a Multicenter Registry-Based Prospective Cohort Study in Germany.

Introduction COVID-19 in pregnancy is associated with increased maternal and neonatal morbidity and mortality. The aim of our study was to investigate the effectiveness of COVID-19 vaccination in SARS-CoV-2-infected pregnant women with focus on women with gestational diabetes mellitus on pregnancy outcomes. Patients and Methods COVID-19 Obstetric and Neonatal Outcome study is a multicenter prospective observational study which registered SARS-CoV-2-infected pregnant women from April 2020 to December 2022. In March 2021, the study was complemented by the SATELLITES study which recruited vaccinated women until September 2023. Primary composite maternal and neonatal endpoints were defined. Multivariate adjusted logistic regression analysis was performed to evaluate the impact of vaccination on pregnancy outcomes. Vaccine effectiveness was defined as (1-adjusted odds ratio)*100. Results We registered 10 386 pregnant women, 6112 of whom were analyzed. 30% of women were vaccinated against COVID-19. Vaccination in women with gestational diabetes mellitus was associated with a vaccine effectiveness of 75% (95% CI: 16 - 93), depending on the predominant virus variant, and of 67% in the total cohort (95% CI: 36 - 83). No statistically significant difference was found in vaccine effectiveness with regards to perinatal outcomes of women with gestational diabetes mellitus (16%; 95% CI -58 - 55) but there was an impact in the total cohort (26%; 95% CI 8 - 94). Conclusion For pregnant women with gestational diabetes mellitus who were infected with SARS-CoV-2, at least one vaccination against COVID-19 before or during pregnancy was independently associated with a milder course of COVID-19 in mothers compared to no vaccination. We found no evidence of improved perinatal outcomes. The data emphasize the benefits of vaccination before or during pregnancy.