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. 2021 Aug 18;74(11):1933–1950. doi: 10.1093/cid/ciab707

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© The Author(s) 2021. Published by Oxford University Press for the Infectious Diseases Society of America.

This is an Open Access article distributed under the terms of the Creative Commons Attribution-NonCommercial-NoDerivs licence (https://creativecommons.org/licenses/by-nc-nd/4.0/), which permits non-commercial reproduction and distribution of the work, in any medium, provided the original work is not altered or transformed in any way, and that the work is properly cited. For commercial re-use, please contact journals.permissions@oup.com

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Figure 2. — Representative histopathological images of heart tissues of mice receiving IV vaccine. Groups of mice were given IV injection of COVID-19 mRNA vaccine (IV group) and NS (NS group) as control. At 1 and 2 dpi, mice were killed for histopathology analysis. A, Low magnification microscopic scanning images of heart sections (4× magnification). Mice received IV NS showed no detectable histological changes in the heart. After IV mRNA vaccine, the scan images showed thickened and dark blue stained visceral pericardium on the surface of right atrium and right ventricle at both 1 and 2 dpi (arrows). B, H&E stain of heart tissue of IV NS group showed no histological damage in the myocardium and cardiomyocytes. C, H&E stained heart tissue showed inflammatory infiltrates of the myocardium at 2 dpi. Arrows indicated infiltrates of inflammatory cells at 400× magnification. D, H&E stained heart tissue of IV vaccine group at 2 dpi showing thickened visceral pericardium with clusters of dark blue crystal-like structure which indicated calcific deposits (arrows) with adjacent inflammatory cell infiltrates and cardiomyocytes degeneration at. 400× magnification. E, H&E stained myocardial tissue showing cardiomyocytes degeneration at 2 dpi in IV group as indicated by arrows at 400× magnification. F, H&E image showing cardiomyocytes necrosis (arrows at 400× magnification) with immune cells infiltration in IV group at 2 dpi. G, Images of immunohistochemistry staining of white blood cells marker CD45, CD68, and CD3 in the heart sections, showing myocardial and visceral pericardial infiltration by CD45 positive cells. Immunostaining of macrophage marker CD68 showed many positives in the infiltrating cells, with less frequently positive CD3 biomarker for T lymphocytes. Abbreviations: COVID-19, coronavirus disease 2019; dpi, days post-injection; H&E, hematoxylin and eosin; IV, intravenous; mRNA, messenger RNA; NS, normal saline.

Figure 2. — Representative histopathological images of heart tissues of mice receiving IV vaccine. Groups of mice were given IV injection of COVID-19 mRNA vaccine (IV group) and NS (NS group) as control. At 1 and 2 dpi, mice were killed for histopathology analysis. A, Low magnification microscopic scanning images of heart sections (4× magnification). Mice received IV NS showed no detectable histological changes in the heart. After IV mRNA vaccine, the scan images showed thickened and dark blue stained visceral pericardium on the surface of right atrium and right ventricle at both 1 and 2 dpi (arrows). B, H&E stain of heart tissue of IV NS group showed no histological damage in the myocardium and cardiomyocytes. C, H&E stained heart tissue showed inflammatory infiltrates of the myocardium at 2 dpi. Arrows indicated infiltrates of inflammatory cells at 400× magnification. D, H&E stained heart tissue of IV vaccine group at 2 dpi showing thickened visceral pericardium with clusters of dark blue crystal-like structure which indicated calcific deposits (arrows) with adjacent inflammatory cell infiltrates and cardiomyocytes degeneration at. 400× magnification. E, H&E stained myocardial tissue showing cardiomyocytes degeneration at 2 dpi in IV group as indicated by arrows at 400× magnification. F, H&E image showing cardiomyocytes necrosis (arrows at 400× magnification) with immune cells infiltration in IV group at 2 dpi. G, Images of immunohistochemistry staining of white blood cells marker CD45, CD68, and CD3 in the heart sections, showing myocardial and visceral pericardial infiltration by CD45 positive cells. Immunostaining of macrophage marker CD68 showed many positives in the infiltrating cells, with less frequently positive CD3 biomarker for T lymphocytes. Abbreviations: COVID-19, coronavirus disease 2019; dpi, days post-injection; H&E, hematoxylin and eosin; IV, intravenous; mRNA, messenger RNA; NS, normal saline.

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