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The SARS-CoV-2 attacks host cells offensively via the respiratory system. In the asymptomatic subjects, the immune cells are active and finally kill the virus (right); whereas in the presymptomatic subjects, the immune cells are slack, the virus evades the attack of the immune system and amplifies quickly, and eventually causes the host to suffer from COVID-19 (left). The image is designed by Shanhe Yu and edited by Lehua Huang. See page 1148-1162 by Shanhe Yu et al. for details.