A child receives a vaccine at a community healthcare center in Qinhuangdao City, north China's Hebei Province. Thursday marks the children's vaccination day in China. (Xinhua/Cao Jianxiong)

A medical worker explains knowledge on vaccination to children at a health center in Dongguocun Township in Xingtai City, north China's Hebei Province, April 25, 2019. Thursday marks the children's vaccination day in China. (Xinhua/Zhang Chi)

A child receives a vaccine at a disease prevention and control center in Xinle City, north China's Hebei Province. Thursday marks the children's vaccination day in China. (Xinhua/Jia Minjie)

A baby receives a vaccine at a maternal and child health care hospital in Handan City, north China's Hebei Province, April 25, 2019. Thursday marks the children's vaccination day in China. (Xinhua/Hao Qunying)

A medical worker explains knowledge on vaccination to people at a maternal and child health care hospital in Handan City, north China's Hebei Province, April 25, 2019. Thursday marks the children's vaccination day in China. (Xinhua/Hao Qunying)

Children try simulated vaccination at a kindergarten in Xingtai City, north China's Hebei Province, April 25, 2019. Thursday marks the children's vaccination day in China. (Xinhua/Zhang Chi)