Recently, with the ups and downs of the domestic and international COVID-19 epidemic, especially the emergence of mutant strains such as Delta, the debate about vaccine and immunity, coexistence and clearance is rampant. Professor Liu Youning, the editor-in-chief of this journal, once suggested that "Chinese people should be universally vaccinated against novel coronavirus and strive to achieve herd immunity as soon as possible", but now why does he say that "the epidemic of mutant strains such as Delta forces us to change our coping strategies"? Please see the Editor-in-Chief's Essay in this issue for details and reasons.