COVID-19 vaccination protects infected pregnant women from developing SARS-CoV-2 placentitis and decreases the risk for stillbirth.

The impact of COVID-19 infection in pregnant women remained unclear for a long time. Previous research showed that SARS-CoV-2 virus is able to infect the placenta, potentially causing significant lesions leading to placental insufficiency. The impact of maternal vaccination status on the prevalence of SARS-CoV-2 placentitis remains unclear. We characterized placental lesions in SARS-CoV-2 infected pregnant women and studied the impact of vaccination on placental involvement. We retrospectively studied 180 placentas sent to the Department of Pathology in UZ Leuven or AZ Turnhout between January 2020 and August 2022, from non-vaccinated and vaccinated mothers suffering a SARS-CoV-2 proven infection during pregnancy. All reports and hematoxylin-eosin stained sections were revised by two pathologists to determine the presence of histopathological lesions that have been described in SARS-CoV-2 infection. SARS-CoV-2 immunostainings were available for a subgroup of 109 placentas. We gathered clinical data: date of delivery, date of positive serologic test result, vaccination status, SARS-CoV-2 variant and outcome of the pregnancy. Of the 180 placentas, 37,2% showed histopathological lesions and in 12,8% an immunohistochemically proven SARS-CoV-2 placentitis was present. SARS-CoV-2 immunohistochemical positivity was only seen in non-vaccinated mothers. The risk of fetal demise was more than 5 times higher for non-vaccinated mothers and their placentas showed significantly more syncytiotrophoblast necrosis and chronic histiocytic intervillositis compared to vaccinated mothers (both p < 0,001). Maternal vaccination was associated with a reduced risk of SARS-CoV-2 placentitis and stillbirth. This study provides new evidence of the protective effect of vaccination on the placenta.

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Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this article.