A medical worker collects a throat swab from a student at a primary school in Xingtai, Hebei province, Jan 6, 2021. The city launched massive nucleic acid testing free of charge after a recent COVID-19 outbreak. (Photo: China Daily)

A medical worker collects a throat swab from a student at a primary school in Xingtai, Hebei province, Jan 6, 2021.

A medical worker collects a throat swab from a student at a secondary school in Xingtai, Hebei province, Jan 6, 2021.

A medical worker collects a throat swab from a girl at a residential community in Xingtai, Hebei province, Jan 6, 2021.

A medical worker conducts a COVID-19 nucleic acid test for a resident at a community in Shijiazhuang, Hebei province on Jan 6, 2021. The city launched a massive round of coronavirus tests following a recent outbreak.

People wait to provide samples for nucleic acid tests for novel coronavirus outside a testing site at a community in Shijiazhuang, Hebei province on Jan 6, 2021.