inclusion criteria: participants are eligible to be included in the study only if the following conditions are met: 1. male or female aged ≥18 years old when signing icf; 2. participants who were fully vaccinated with 2 or 3 doses of mrna covid-19 vaccine (comirnaty). the interval between the last dose and this study vaccination is 4 to 12 months; 3. the participant and/or his entrusted person can sign written icf, and can fully understand the trial procedure, the risk of participating in the trial, and other interventions that can be selected if they do not participate in the trial; 4. the participant and/or his entrusted person has the ability to read, understand, and fill in record cards; 5. healthy participants or participants with pre-existing medical conditions who are in stable condition. the "pre-existing medical conditions" include but not limited to hypertension, diabetes, chronic cholecystitis and cholelithiasis, chronic gastritis that meet the described criteria. a stable medical condition is defined as disease not requiring significant change in therapy or no need for hospitalization as a consequence of worsening disease state for at least 3 months prior to enrollment; 6. fertile men and women of childbearing potential voluntarily agree to take effective contraceptive measures from signing icf to 6 months after the study vaccination; the pregnancy test results of women of childbearing potential are negative on screening.

inclusion criteria: participants are eligible to be included in the study only if the following conditions are met: 1. male or female aged ≥18 years old when signing icf; 2. participants who were fully vaccinated with 2 or 3 doses of mrna covid-19 vaccine (comirnaty). the interval between the last dose and this study vaccination is 4 to 12 months; 3. the participant and/or his entrusted person can sign written icf, and can fully understand the trial procedure, the risk of participating in the trial, and other interventions that can be selected if they do not participate in the trial; 4. the participant and/or his entrusted person has the ability to read, understand, and fill in record cards; 5. healthy participants or participants with pre-existing medical conditions who are in stable condition. the "pre-existing medical conditions" include but not limited to hypertension, diabetes, chronic cholecystitis and cholelithiasis, chronic gastritis that meet the described criteria. a stable medical condition is defined as disease not requiring significant change in therapy or no need for hospitalization as a consequence of worsening disease state for at least 3 months prior to enrollment; 6. fertile men and women of childbearing potential voluntarily agree to take effective contraceptive measures from signing icf to 6 months after the study vaccination; the pregnancy test results of women of childbearing potential are negative on screening.

inclusion criteria: participants are eligible to be included in the study only if the following conditions are met: male or female aged ≥18 years old when signing icf; participants who were fully vaccinated with 2 or 3 doses of mrna covid-19 vaccine (comirnaty). the interval between the last dose and this study vaccination is 4 to 12 months; the participant and/or his entrusted person can sign written icf, and can fully understand the trial procedure, the risk of participating in the trial, and other interventions that can be selected if they do not participate in the trial; the participant and/or his entrusted person has the ability to read, understand, and fill in record cards; healthy participants or participants with pre-existing medical conditions who are in stable condition. the "pre-existing medical conditions" include but not limited to hypertension, diabetes, chronic cholecystitis and cholelithiasis, chronic gastritis that meet the described criteria. a stable medical condition is defined as disease not requiring significant change in therapy or no need for hospitalization as a consequence of worsening disease state for at least 3 months prior to enrollment; fertile men and women of childbearing potential voluntarily agree to take effective contraceptive measures from signing icf to 6 months after the study vaccination; the pregnancy test results of women of childbearing potential are negative on screening.

inclusion criteria: participants are eligible to be included in the study only if the following conditions are met: male or female aged ≥18 years old when signing icf; participants who were fully vaccinated with 2 or 3 doses of mrna covid-19 vaccine (comirnaty). the interval between the last dose and this study vaccination is 4 to 12 months; the participant and/or his entrusted person can sign written icf, and can fully understand the trial procedure, the risk of participating in the trial, and other interventions that can be selected if they do not participate in the trial; the participant and/or his entrusted person has the ability to read, understand, and fill in record cards; healthy participants or participants with pre-existing medical conditions who are in stable condition. the "pre-existing medical conditions" include but not limited to hypertension, diabetes, chronic cholecystitis and cholelithiasis, chronic gastritis that meet the described criteria. a stable medical condition is defined as disease not requiring significant change in therapy or no need for hospitalization as a consequence of worsening disease state for at least 3 months prior to enrollment; fertile men and women of childbearing potential voluntarily agree to take effective contraceptive measures from signing icf to 6 months after the study vaccination; the pregnancy test results of women of childbearing potential are negative on screening.