inclusion criteria: - voluntarily participate in the study and sign the informed consent form - the participants who were enrolled in the 10 μg test group in the previous study titled "a randomized, double-blind, placebo-controlled phase i clinical trial to evaluate the safety and immunogenicity of recombinant sars-cov-2 fusion protein vaccine (v-01) in healthy participants", and went through the full course immunization without meeting the exclusive criteria. - no history of contact with confirmed, asymptomatic or suspected covid-19 cases. - males of reproductive potential and females of childbearing potential voluntarily agree to take effective and acceptable contraceptive methods from the signing of informed consent form to 6 months after vaccination; females of childbearing age refer to premenopausal women and women within 2 years after menopause.

inclusion criteria: - voluntarily participate in the study and sign the informed consent form - the participants who were enrolled in the 10 μg test group in the previous study titled "a randomized, double-blind, placebo-controlled phase i clinical trial to evaluate the safety and immunogenicity of recombinant sars-cov-2 fusion protein vaccine (v-01) in healthy participants", and went through the full course immunization without meeting the exclusive criteria. - no history of contact with confirmed, asymptomatic or suspected covid-19 cases. - males of reproductive potential and females of childbearing potential voluntarily agree to take effective and acceptable contraceptive methods from the signing of informed consent form to 6 months after vaccination; females of childbearing age refer to premenopausal women and women within 2 years after menopause.