inclusion criteria: healthy adults aged 18 years and above; subjects completed two doses of the prototype covid-19 vaccine (cz strain)(the interval between the first dose and the second dose was 1-2 months)or completed 3 doses of prototype covid-19 vaccine (cz strain)over 6 months (the interval between the first dose and the second dose was 1-2 months, and the interval between the second dose and the third dose was 6 months or more); the subjects can understand and voluntarily sign the informed consent form; provide legal identification and vaccination certificate of prototype covid-19 vaccine (cz strain).

inclusion criteria: healthy adults aged 18 years and above; subjects completed two doses of the prototype covid-19 vaccine (cz strain)(the interval between the first dose and the second dose was 1-2 months)or completed 3 doses of prototype covid-19 vaccine (cz strain)over 6 months (the interval between the first dose and the second dose was 1-2 months, and the interval between the second dose and the third dose was 6 months or more); the subjects can understand and voluntarily sign the informed consent form; provide legal identification and vaccination certificate of prototype covid-19 vaccine (cz strain).

inclusion criteria: healthy adults aged 18 years and above; subjects completed two doses of the prototype covid-19 vaccine(the interval between the first dose and the second dose was 1-2 months)or completed 3 doses of prototype covid-19 vaccine over 6 months (the interval between the first dose and the second dose was 1-2 months, and the interval between the second dose and the third dose was 6 months or more); the subjects can understand and voluntarily sign the informed consent form; provide legal identification and vaccination certificate of prototype covid-19 vaccine.

inclusion criteria: healthy adults aged 18 years and above; subjects completed two doses of the prototype covid-19 vaccine(the interval between the first dose and the second dose was 1-2 months)or completed 3 doses of prototype covid-19 vaccine over 6 months (the interval between the first dose and the second dose was 1-2 months, and the interval between the second dose and the third dose was 6 months or more); the subjects can understand and voluntarily sign the informed consent form; provide legal identification and vaccination certificate of prototype covid-19 vaccine.