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Girls pose for photos with their COVID-19 vaccination stickers after being vaccinated at a vaccination site in Toronto, Canada, on Dec. 12, 2021. The City of Toronto on Sunday hosted a superhero-themed mass vaccination event as Toronto Kids Vaccine Day to vaccinate up to 2,000 children aged five to 11 against COVID-19. (Photo: Xinhua/Zou Zheng)
![](http://www.ecns.cn/hd/2021/12/13/73a4c2c896aa40eab60d237702197934.jpg)
A vaccinator wearing a face mask and a face shield administers the COVID-19 vaccine to a child at a vaccination site in Toronto, Canada, on Dec. 12, 2021. The City of Toronto on Sunday hosted a superhero-themed mass vaccination event as Toronto Kids Vaccine Day to vaccinate up to 2,000 children aged five to 11 against COVID-19. (Photo: Xinhua/Zou Zheng)
![](http://www.ecns.cn/hd/2021/12/13/4224f8e444d44cf8b3179848d774348b.jpg)
A vaccinator wearing a face mask and a face shield prepares to administer the COVID-19 vaccine to a child at a vaccination site in Toronto, Canada, on Dec. 12, 2021. The City of Toronto on Sunday hosted a superhero-themed mass vaccination event as Toronto Kids Vaccine Day to vaccinate up to 2,000 children aged five to 11 against COVID-19. (Photo: Xinhua/Zou Zheng)
![](http://www.ecns.cn/hd/2021/12/13/98a403f085754874b1a43decb97f5396.jpg)
Children receive the COVID-19 vaccine at a vaccination site in Toronto, Canada, on Dec. 12, 2021. The City of Toronto on Sunday hosted a superhero-themed mass vaccination event as Toronto Kids Vaccine Day to vaccinate up to 2,000 children aged five to 11 against COVID-19. (Photo: Xinhua/Zou Zheng)
![](http://www.ecns.cn/hd/2021/12/13/dded4af97f244b53868a43df05b9eec6.jpg)
Children receive the COVID-19 vaccine at a vaccination site in Toronto, Canada, on Dec. 12, 2021. The City of Toronto on Sunday hosted a superhero-themed mass vaccination event as Toronto Kids Vaccine Day to vaccinate up to 2,000 children aged five to 11 against COVID-19. (Photo: Xinhua/Zou Zheng)
![](http://www.ecns.cn/hd/2021/12/13/7f7bfece810945f8bc0e01537a81cb5d.jpg)
A boy wearing a face mask poses for photos with a COVID-19 vaccination "passport" after being vaccinated outside a vaccination site in Toronto, Canada, on Dec. 12, 2021. The City of Toronto on Sunday hosted a superhero-themed mass vaccination event as Toronto Kids Vaccine Day to vaccinate up to 2,000 children aged five to 11 against COVID-19. (Photo: Xinhua/Zou Zheng)