Medical workers wearing cartoon head decorations work at a vaccination site in Xuhui District of Shanghai, east China, Nov. 20, 2021. Shanghai started COVID-19 vaccination for children aged 3-5 from Saturday. (Xinhua/Liu Ying)

A four-year-old girl receives COVID-19 vaccine at a vaccination site in Xuhui District of Shanghai, east China, Nov. 20, 2021. Shanghai started COVID-19 vaccination for children aged 3-5 from Saturday. (Xinhua/Liu Ying)

A medical worker gives thumb up to a child at a vaccination site in Xuhui District of Shanghai, east China, Nov. 20, 2021. Shanghai started COVID-19 vaccination for children aged 3-5 from Saturday. (Xinhua/Liu Ying)

A staff member in cartoon costume comforts a boy at a vaccination site in Xuhui District of Shanghai, east China, Nov. 20, 2021. Shanghai started COVID-19 vaccination for children aged 3-5 from Saturday. (Xinhua/Liu Ying)

A five-year-old girl, accompanied by her father and brother, gets vaccinated at a vaccination site in Xuhui District of Shanghai, east China, Nov. 20, 2021. Shanghai started COVID-19 vaccination for children aged 3-5 from Saturday. (Xinhua/Liu Ying)

A medical worker writes on an information card which is specially made for children at a vaccination site in Xuhui District of Shanghai, east China, Nov. 20, 2021. Shanghai started COVID-19 vaccination for children aged 3-5 from Saturday. (Xinhua/Liu Ying)

A medical worker wearing cartoon head decoration works at a vaccination site in Xuhui District of Shanghai, east China, Nov. 20, 2021. Shanghai started COVID-19 vaccination for children aged 3-5 from Saturday. (Xinhua/Liu Ying)