American Journal of Reproductive Immunology: Decreased severity of COVID-19 in vaccinated pregnant individuals during predominance of different SARS-CoV-2 variants



Since the start of the pandemic, Pregnant individuals have been disproportionately affected by the severe acute respiratory syndrome coronavirus 2. Vaccination has been shown to be protective against severe disease. However, data on effectiveness of vaccine in reducing disease severity are limited in pregnant individuals who later developed COVID-19.

Method of study

This is a single academic center retrospective cohort study of pregnant individuals who tested positive for COVID-19 from December 2020 through January 2022. The cohort was divided into two groups based on vaccination status. The primary outcome of our study was progression to severe or critical disease. A secondary analysis was performed based on the timeframes of predominance of different variants of SARS-CoV-2, to determine whether the effect of vaccination was different during these epochs.


Our cohort included 472 patients among which 125 (26.5%) were vaccinated and 347 were unvaccinated. None of the patients in the vaccinated group who later developed COVID-19 progressed to severe or critical disease compared to 7.2% in the unvaccinated one (p < .01). Similarly, after adjusting for medical comorbidities, obesity, receipt of monoclonal antibodies, and trimester at diagnosis, vaccinated individuals who later developed COVID-19 were less likely to be admitted to the hospital (1.6% vs. 14.7%, aOR .14, 95% CI .22–.47) compared with unvaccinated ones.


Vaccination against SARS-CoV-2 in pregnant individuals who later develop a breakthrough infection, is associated with decreased progression to severe or critical COVID-19, and need for hospital and ICU admissions. Vaccination is specifically effective during the predominance of the more severe Delta variant.

First published: 05 July 2022