inclusion criteria: * participated in "a phase iii randomized, double-blind, placebo-controlled clinical trial in 18 years of age and above to determine the safety and efficacy of zf2001, a recombinant novel coronavirus vaccine (cho cell) for prevention of covid-19. protocol no.: lkm-2020-ncv-gj01)" and has completed basic immunization with recombinant novel coronavirus vaccine (cho cells) since 12 months (window period ± 3 months); * the subjects voluntarily participate in the study, sign an informed consent form, and can provide valid identification, understand and comply with the requirements of the trial protocol; * female subjects of childbearing age agree to take effective contraceptive measures from the start of the study to 1 month after vaccination.

inclusion criteria: * participated in "a phase iii randomized, double-blind, placebo-controlled clinical trial in 18 years of age and above to determine the safety and efficacy of zf2001, a recombinant novel coronavirus vaccine (cho cell) for prevention of covid-19. protocol no.: lkm-2020-ncv-gj01)" and has completed basic immunization with recombinant novel coronavirus vaccine (cho cells) since 12 months (window period ± 3 months); * the subjects voluntarily participate in the study, sign an informed consent form, and can provide valid identification, understand and comply with the requirements of the trial protocol; * female subjects of childbearing age agree to take effective contraceptive measures from the start of the study to 1 month after vaccination.

inclusion criteria: participated in "a phase iii randomized, double-blind, placebo-controlled clinical trial in 18 years of age and above to determine the safety and efficacy of zf2001, a recombinant novel coronavirus vaccine (cho cell) for prevention of covid-19. protocol no.: lkm-2020-ncv-gj01)" and has completed basic immunization with recombinant novel coronavirus vaccine (cho cells) since 12 months (window period ± 3 months); the subjects voluntarily participate in the study, sign an informed consent form, and can provide valid identification, understand and comply with the requirements of the trial protocol; female subjects of childbearing age agree to take effective contraceptive measures from the start of the study to 1 month after vaccination.

inclusion criteria: participated in "a phase iii randomized, double-blind, placebo-controlled clinical trial in 18 years of age and above to determine the safety and efficacy of zf2001, a recombinant novel coronavirus vaccine (cho cell) for prevention of covid-19. protocol no.: lkm-2020-ncv-gj01)" and has completed basic immunization with recombinant novel coronavirus vaccine (cho cells) since 12 months (window period ± 3 months); the subjects voluntarily participate in the study, sign an informed consent form, and can provide valid identification, understand and comply with the requirements of the trial protocol; female subjects of childbearing age agree to take effective contraceptive measures from the start of the study to 1 month after vaccination.