for adult group (age ≥18 and ≤55) * have had any acute illness, as determined by the investigator, with or without fever, within 72 hours prior to the prime vaccination. an acute illness which is nearly resolved with only minor residual symptoms remaining is allowable if, in the opinion of the investigator, the residual symptoms will not compromise their well-being if they participate as trial subjects in the trial, or that could prevent, limit, or confound the protocol-specified assessments. * are breastfeeding on the day of screening visit or who plan to breastfeed during the trial, starting from screening visit and continuously until at least 90 days after the last immunization. women or partners who plan to become pregnant within 1 year post the screening visit. * have a known allergy, hypersensitivity, or intolerance to the planned vaccine for trial including any excipients. * used to have a history of hypersensitivity or serious reactions to vaccination. * received any vaccination within 4 weeks prior to visit 1. * don't agree to not be vaccinated during the trial, starting from screening visit and continuously until 28 days after receiving the last immunization, except emergency vaccination (e.g. rabies vaccine, tetanus vaccine). * had any medical condition (e.g., autoimmune disease) or any major surgery (e.g., requiring general anesthesia) within the past 5 years, which in the opinion of the investigator, could compromise their well-being if they participate as trial subjects in the trial, or that could prevent, limit, or confound the protocol-specified assessments. * have any surgery planned during the trial, starting from screening visit and continuously until at least 90 days after the last immunization. * had any chronic use (more than 14 continuous days) of any systemic medications that affects immune function, including immunosuppressant or other immune-modifying drugs, within 6 months prior to screening visit unless in the opinion of the investigator, the medication would not prevent, limit, or confound the protocol-specified assessments or could compromise safety of subjects. * had administration of any immunoglobulins and/or any blood products within the 3 months prior to screening visit. * had administration of another investigational product including vaccines within 60 days or 5 half-lives (whichever is longer), prior to screening visit. * with known history of aids or human immunodeficiency virus (hiv) test positive. * history of hepatitis b virus (hbv) or hepatitis c virus (hcv) infection, through medical inquiry. * history of sars, sars-cov-2 or middle east respiratory syndrome (mers) infection. suspected sars patients should be screened for sars antibodies. * previously participated in a clinical trial involving lipid nanoparticles. * are subject to exclusion periods of other clinical trials or simultaneous participation in another clinical trial. * have any affiliation with the study site (e.g., are close relative of the investigator or dependent person, such as an employee or student of the study site). * have a history of drug abuse or known medical, psychological, or social conditions within the past 5 years. in the opinion of the investigator, could comprise their well-being if they participate as trial subjects in the trial, or that could prevent, limit, or confound the protocol-specified assessments. * have a history of narcolepsy. * have history of alcohol abuse or drug addiction within 1 year prior to screening visit. * have a history of or suspected immunosuppressive condition, acquired or congenital, as determined by medical history and/or physical examination at screening visit. * have any abnormality or permanent body art (e.g., tattoo), that in the opinion of the investigator, would obstruct the ability to observe local reactions at the vaccination site. * have had any blood loss \>400 ml, e.g., due to donation of blood or blood products or injury, within the 28 days prior to screening visit or plan to donate blood or plasma during the trial, starting from screening visit and continuously until at least 28 days after being given the last immunization. * travel or live in any country or region with a high sars-cov-2 infection risk (as defined at screening visit) within the 14 days prior to screening visit. * they plan to visit any country or region with a high sars-cov-2 infection risk (as defined at screening visit), from screening visit until 14 days after being given the last immunization. * symptoms of covid-19, e.g., respiratory symptoms, fever, cough, shortness of breath and breathing difficulties. * have had contact with confirmed covid-19 patients or persons tested positive for sars-cov-2 within the 30 days prior to screening visit. * are vulnerable persons, e.g., soldiers, subjects in detention, contract research organization (cro) or fosun staff or their family members. for the elderly group (age ≥65 and ≤85) * baseline laboratory abnormalities with grade ≥3 (for hematology abnormalities with grade ≥2) during screening visits, by physical examination and eligibility screening. * have had any acute illness, as determined by the investigator, with or without fever, within 72 hours prior to the prime vaccination. an acute illness which is nearly resolved with only minor residual symptoms remaining is allowable if, in the opinion of the investigator, the residual symptoms will not compromise their well-being if they participate as trial subjects in the trial, or that will not prevent, limit, or confound the protocol-specified assessments. * have a known allergy, hypersensitivity, or intolerance to the planned vaccine for trial including any excipients. * used to have a history of hypersensitivity or serious reactions to vaccination. * received any vaccination within 4 weeks prior to visit 1. * don't agree to not be vaccinated during the trial, starting from screening visit and continuously until 28 days after receiving the last immunization, except emergency vaccination (e.g. rabies vaccine, tetanus vaccine). * had administration of any immunoglobulins and/or any blood products within the 3 months prior to screening visit. * had any serious or life-threatening medical condition (e.g., autoimmune disease, cardiovascular disease) within the past 5 years, which in the opinion of the investigator, could compromise their well-being if they participate as trial subjects in the trial, or that could prevent, limit, or confound the protocol-specified assessments. * have any surgery planned during the trial, starting from screening visit and continuously until at least 90 days after the last immunization. * had any chronic use (more than 14 continuous days) of any systemic medications that affects immune function, including immunosuppressant or other immune-modifying drugs, within 6 months prior to screening visit unless in the opinion of the investigator, the medication would not prevent, limit, or confound the protocol-specified assessments or could compromise safety of subjects. * had administration of another investigational product including vaccines within 60 days or 5 half-lives (whichever is longer), prior to screening visit. * with known history of aids or hiv test positive. * history of hbv or hcv infection. * history of sars, sars-cov-2 or mers infection. suspected sars patients should be screened for sars antibodies. * previously participated in a clinical trial involving lipid nanoparticles. * are subject to exclusion periods of other clinical trials or simultaneous participation in another clinical trial. * have any affiliation with the study site (e.g., are close relative of the investigator or dependent person, such as an employee or student of the study site). * have a history of drug abuse or known medical, psychological, or social conditions within the past 5 years. in the opinion of the investigator, could comprise their well-being if they participate as trial subjects in the trial, or that could prevent, limit, or confound the protocol-specified assessments. * have a history of narcolepsy. * have history of alcohol abuse or drug addiction within 1 year prior to screening visit. * have a history of or suspected immunosuppressive condition, acquired or congenital, as determined by medical history and/or physical examination at screening visit. * have any abnormality or permanent body art (e.g., tattoo), that in the opinion of the investigator, would obstruct the ability to observe local reactions at the vaccination site. * have had any blood loss \>400 ml, e.g., due to donation of blood or blood products or injury, within the 28 days prior to screening visit or plan to donate blood or plasma during the trial, starting from screening visit and continuously until at least 28 days after being given the last immunization. * travel or live in any country or region with a high sars-cov-2 infection risk (as defined at screening visit) within the 14 days prior to screening visit. * they plan to visit any country or region with a high sars-cov-2 infection risk (as defined at screening visit), from screening visit until 14 days after being given the last immunization. * symptoms of covid-19, e.g., respiratory symptoms, fever, cough, shortness of breath and breathing difficulties. * have had contact with confirmed covid-19 patients or persons tested positive for sars-cov-2 nucleic acids or antibodies within the 30 days prior to screening visit. * are vulnerable persons, e.g., soldiers, subjects in detention, cro or fosun staff or their family members.

for adult group (age ≥18 and ≤55) * have had any acute illness, as determined by the investigator, with or without fever, within 72 hours prior to the prime vaccination. an acute illness which is nearly resolved with only minor residual symptoms remaining is allowable if, in the opinion of the investigator, the residual symptoms will not compromise their well-being if they participate as trial subjects in the trial, or that could prevent, limit, or confound the protocol-specified assessments. * are breastfeeding on the day of screening visit or who plan to breastfeed during the trial, starting from screening visit and continuously until at least 90 days after the last immunization. women or partners who plan to become pregnant within 1 year post the screening visit. * have a known allergy, hypersensitivity, or intolerance to the planned vaccine for trial including any excipients. * used to have a history of hypersensitivity or serious reactions to vaccination. * received any vaccination within 4 weeks prior to visit 1. * don't agree to not be vaccinated during the trial, starting from screening visit and continuously until 28 days after receiving the last immunization, except emergency vaccination (e.g. rabies vaccine, tetanus vaccine). * had any medical condition (e.g., autoimmune disease) or any major surgery (e.g., requiring general anesthesia) within the past 5 years, which in the opinion of the investigator, could compromise their well-being if they participate as trial subjects in the trial, or that could prevent, limit, or confound the protocol-specified assessments. * have any surgery planned during the trial, starting from screening visit and continuously until at least 90 days after the last immunization. * had any chronic use (more than 14 continuous days) of any systemic medications that affects immune function, including immunosuppressant or other immune-modifying drugs, within 6 months prior to screening visit unless in the opinion of the investigator, the medication would not prevent, limit, or confound the protocol-specified assessments or could compromise safety of subjects. * had administration of any immunoglobulins and/or any blood products within the 3 months prior to screening visit. * had administration of another investigational product including vaccines within 60 days or 5 half-lives (whichever is longer), prior to screening visit. * with known history of aids or human immunodeficiency virus (hiv) test positive. * history of hepatitis b virus (hbv) or hepatitis c virus (hcv) infection, through medical inquiry. * history of sars, sars-cov-2 or middle east respiratory syndrome (mers) infection. suspected sars patients should be screened for sars antibodies. * previously participated in a clinical trial involving lipid nanoparticles. * are subject to exclusion periods of other clinical trials or simultaneous participation in another clinical trial. * have any affiliation with the study site (e.g., are close relative of the investigator or dependent person, such as an employee or student of the study site). * have a history of drug abuse or known medical, psychological, or social conditions within the past 5 years. in the opinion of the investigator, could comprise their well-being if they participate as trial subjects in the trial, or that could prevent, limit, or confound the protocol-specified assessments. * have a history of narcolepsy. * have history of alcohol abuse or drug addiction within 1 year prior to screening visit. * have a history of or suspected immunosuppressive condition, acquired or congenital, as determined by medical history and/or physical examination at screening visit. * have any abnormality or permanent body art (e.g., tattoo), that in the opinion of the investigator, would obstruct the ability to observe local reactions at the vaccination site. * have had any blood loss \>400 ml, e.g., due to donation of blood or blood products or injury, within the 28 days prior to screening visit or plan to donate blood or plasma during the trial, starting from screening visit and continuously until at least 28 days after being given the last immunization. * travel or live in any country or region with a high sars-cov-2 infection risk (as defined at screening visit) within the 14 days prior to screening visit. * they plan to visit any country or region with a high sars-cov-2 infection risk (as defined at screening visit), from screening visit until 14 days after being given the last immunization. * symptoms of covid-19, e.g., respiratory symptoms, fever, cough, shortness of breath and breathing difficulties. * have had contact with confirmed covid-19 patients or persons tested positive for sars-cov-2 within the 30 days prior to screening visit. * are vulnerable persons, e.g., soldiers, subjects in detention, contract research organization (cro) or fosun staff or their family members. for the elderly group (age ≥65 and ≤85) * baseline laboratory abnormalities with grade ≥3 (for hematology abnormalities with grade ≥2) during screening visits, by physical examination and eligibility screening. * have had any acute illness, as determined by the investigator, with or without fever, within 72 hours prior to the prime vaccination. an acute illness which is nearly resolved with only minor residual symptoms remaining is allowable if, in the opinion of the investigator, the residual symptoms will not compromise their well-being if they participate as trial subjects in the trial, or that will not prevent, limit, or confound the protocol-specified assessments. * have a known allergy, hypersensitivity, or intolerance to the planned vaccine for trial including any excipients. * used to have a history of hypersensitivity or serious reactions to vaccination. * received any vaccination within 4 weeks prior to visit 1. * don't agree to not be vaccinated during the trial, starting from screening visit and continuously until 28 days after receiving the last immunization, except emergency vaccination (e.g. rabies vaccine, tetanus vaccine). * had administration of any immunoglobulins and/or any blood products within the 3 months prior to screening visit. * had any serious or life-threatening medical condition (e.g., autoimmune disease, cardiovascular disease) within the past 5 years, which in the opinion of the investigator, could compromise their well-being if they participate as trial subjects in the trial, or that could prevent, limit, or confound the protocol-specified assessments. * have any surgery planned during the trial, starting from screening visit and continuously until at least 90 days after the last immunization. * had any chronic use (more than 14 continuous days) of any systemic medications that affects immune function, including immunosuppressant or other immune-modifying drugs, within 6 months prior to screening visit unless in the opinion of the investigator, the medication would not prevent, limit, or confound the protocol-specified assessments or could compromise safety of subjects. * had administration of another investigational product including vaccines within 60 days or 5 half-lives (whichever is longer), prior to screening visit. * with known history of aids or hiv test positive. * history of hbv or hcv infection. * history of sars, sars-cov-2 or mers infection. suspected sars patients should be screened for sars antibodies. * previously participated in a clinical trial involving lipid nanoparticles. * are subject to exclusion periods of other clinical trials or simultaneous participation in another clinical trial. * have any affiliation with the study site (e.g., are close relative of the investigator or dependent person, such as an employee or student of the study site). * have a history of drug abuse or known medical, psychological, or social conditions within the past 5 years. in the opinion of the investigator, could comprise their well-being if they participate as trial subjects in the trial, or that could prevent, limit, or confound the protocol-specified assessments. * have a history of narcolepsy. * have history of alcohol abuse or drug addiction within 1 year prior to screening visit. * have a history of or suspected immunosuppressive condition, acquired or congenital, as determined by medical history and/or physical examination at screening visit. * have any abnormality or permanent body art (e.g., tattoo), that in the opinion of the investigator, would obstruct the ability to observe local reactions at the vaccination site. * have had any blood loss \>400 ml, e.g., due to donation of blood or blood products or injury, within the 28 days prior to screening visit or plan to donate blood or plasma during the trial, starting from screening visit and continuously until at least 28 days after being given the last immunization. * travel or live in any country or region with a high sars-cov-2 infection risk (as defined at screening visit) within the 14 days prior to screening visit. * they plan to visit any country or region with a high sars-cov-2 infection risk (as defined at screening visit), from screening visit until 14 days after being given the last immunization. * symptoms of covid-19, e.g., respiratory symptoms, fever, cough, shortness of breath and breathing difficulties. * have had contact with confirmed covid-19 patients or persons tested positive for sars-cov-2 nucleic acids or antibodies within the 30 days prior to screening visit. * are vulnerable persons, e.g., soldiers, subjects in detention, cro or fosun staff or their family members.

for adult group (age ≥18 and ≤55) - have had any acute illness, as determined by the investigator, with or without fever, within 72 hours prior to the prime vaccination. an acute illness which is nearly resolved with only minor residual symptoms remaining is allowable if, in the opinion of the investigator, the residual symptoms will not compromise their well-being if they participate as trial subjects in the trial, or that could prevent, limit, or confound the protocol-specified assessments. - are breastfeeding on the day of screening visit or who plan to breastfeed during the trial, starting from screening visit and continuously until at least 90 days after the last immunization. women or partners who plan to become pregnant within 1 year post the screening visit. - have a known allergy, hypersensitivity, or intolerance to the planned vaccine for trial including any excipients. - used to have a history of hypersensitivity or serious reactions to vaccination. - received any vaccination within 4 weeks prior to visit 1. - don't agree to not be vaccinated during the trial, starting from screening visit and continuously until 28 days after receiving the last immunization, except emergency vaccination (e.g. rabies vaccine, tetanus vaccine). - had any medical condition (e.g., autoimmune disease) or any major surgery (e.g., requiring general anesthesia) within the past 5 years, which in the opinion of the investigator, could compromise their well-being if they participate as trial subjects in the trial, or that could prevent, limit, or confound the protocol-specified assessments. - have any surgery planned during the trial, starting from screening visit and continuously until at least 90 days after the last immunization. - had any chronic use (more than 14 continuous days) of any systemic medications that affects immune function, including immunosuppressant or other immune-modifying drugs, within 6 months prior to screening visit unless in the opinion of the investigator, the medication would not prevent, limit, or confound the protocol-specified assessments or could compromise safety of subjects. - had administration of any immunoglobulins and/or any blood products within the 3 months prior to screening visit. - had administration of another investigational product including vaccines within 60 days or 5 half-lives (whichever is longer), prior to screening visit. - with known history of aids or human immunodeficiency virus (hiv) test positive. - history of hepatitis b virus (hbv) or hepatitis c virus (hcv) infection, through medical inquiry. - history of sars, sars-cov-2 or middle east respiratory syndrome (mers) infection. suspected sars patients should be screened for sars antibodies. - previously participated in a clinical trial involving lipid nanoparticles. - are subject to exclusion periods of other clinical trials or simultaneous participation in another clinical trial. - have any affiliation with the study site (e.g., are close relative of the investigator or dependent person, such as an employee or student of the study site). - have a history of drug abuse or known medical, psychological, or social conditions within the past 5 years. in the opinion of the investigator, could comprise their well-being if they participate as trial subjects in the trial, or that could prevent, limit, or confound the protocol-specified assessments. - have a history of narcolepsy. - have history of alcohol abuse or drug addiction within 1 year prior to screening visit. - have a history of or suspected immunosuppressive condition, acquired or congenital, as determined by medical history and/or physical examination at screening visit. - have any abnormality or permanent body art (e.g., tattoo), that in the opinion of the investigator, would obstruct the ability to observe local reactions at the vaccination site. - have had any blood loss >400 ml, e.g., due to donation of blood or blood products or injury, within the 28 days prior to screening visit or plan to donate blood or plasma during the trial, starting from screening visit and continuously until at least 28 days after being given the last immunization. - travel or live in any country or region with a high sars-cov-2 infection risk (as defined at screening visit) within the 14 days prior to screening visit. - they plan to visit any country or region with a high sars-cov-2 infection risk (as defined at screening visit), from screening visit until 14 days after being given the last immunization. - symptoms of covid-19, e.g., respiratory symptoms, fever, cough, shortness of breath and breathing difficulties. - have had contact with confirmed covid-19 patients or persons tested positive for sars-cov-2 within the 30 days prior to screening visit. - are vulnerable persons, e.g., soldiers, subjects in detention, contract research organization (cro) or fosun staff or their family members. for the elderly group (age ≥65 and ≤85) - baseline laboratory abnormalities with grade ≥3 (for hematology abnormalities with grade ≥2) during screening visits, by physical examination and eligibility screening. - have had any acute illness, as determined by the investigator, with or without fever, within 72 hours prior to the prime vaccination. an acute illness which is nearly resolved with only minor residual symptoms remaining is allowable if, in the opinion of the investigator, the residual symptoms will not compromise their well-being if they participate as trial subjects in the trial, or that will not prevent, limit, or confound the protocol-specified assessments. - have a known allergy, hypersensitivity, or intolerance to the planned vaccine for trial including any excipients. - used to have a history of hypersensitivity or serious reactions to vaccination. - received any vaccination within 4 weeks prior to visit 1. - don't agree to not be vaccinated during the trial, starting from screening visit and continuously until 28 days after receiving the last immunization, except emergency vaccination (e.g. rabies vaccine, tetanus vaccine). - had administration of any immunoglobulins and/or any blood products within the 3 months prior to screening visit. - had any serious or life-threatening medical condition (e.g., autoimmune disease, cardiovascular disease) within the past 5 years, which in the opinion of the investigator, could compromise their well-being if they participate as trial subjects in the trial, or that could prevent, limit, or confound the protocol-specified assessments. - have any surgery planned during the trial, starting from screening visit and continuously until at least 90 days after the last immunization. - had any chronic use (more than 14 continuous days) of any systemic medications that affects immune function, including immunosuppressant or other immune-modifying drugs, within 6 months prior to screening visit unless in the opinion of the investigator, the medication would not prevent, limit, or confound the protocol-specified assessments or could compromise safety of subjects. - had administration of another investigational product including vaccines within 60 days or 5 half-lives (whichever is longer), prior to screening visit. - with known history of aids or hiv test positive. - history of hbv or hcv infection. - history of sars, sars-cov-2 or mers infection. suspected sars patients should be screened for sars antibodies. - previously participated in a clinical trial involving lipid nanoparticles. - are subject to exclusion periods of other clinical trials or simultaneous participation in another clinical trial. - have any affiliation with the study site (e.g., are close relative of the investigator or dependent person, such as an employee or student of the study site). - have a history of drug abuse or known medical, psychological, or social conditions within the past 5 years. in the opinion of the investigator, could comprise their well-being if they participate as trial subjects in the trial, or that could prevent, limit, or confound the protocol-specified assessments. - have a history of narcolepsy. - have history of alcohol abuse or drug addiction within 1 year prior to screening visit. - have a history of or suspected immunosuppressive condition, acquired or congenital, as determined by medical history and/or physical examination at screening visit. - have any abnormality or permanent body art (e.g., tattoo), that in the opinion of the investigator, would obstruct the ability to observe local reactions at the vaccination site. - have had any blood loss >400 ml, e.g., due to donation of blood or blood products or injury, within the 28 days prior to screening visit or plan to donate blood or plasma during the trial, starting from screening visit and continuously until at least 28 days after being given the last immunization. - travel or live in any country or region with a high sars-cov-2 infection risk (as defined at screening visit) within the 14 days prior to screening visit. - they plan to visit any country or region with a high sars-cov-2 infection risk (as defined at screening visit), from screening visit until 14 days after being given the last immunization. - symptoms of covid-19, e.g., respiratory symptoms, fever, cough, shortness of breath and breathing difficulties. - have had contact with confirmed covid-19 patients or persons tested positive for sars-cov-2 nucleic acids or antibodies within the 30 days prior to screening visit. - are vulnerable persons, e.g., soldiers, subjects in detention, cro or fosun staff or their family members.

for adult group (age ≥18 and ≤55) - have had any acute illness, as determined by the investigator, with or without fever, within 72 hours prior to the prime vaccination. an acute illness which is nearly resolved with only minor residual symptoms remaining is allowable if, in the opinion of the investigator, the residual symptoms will not compromise their well-being if they participate as trial subjects in the trial, or that could prevent, limit, or confound the protocol-specified assessments. - are breastfeeding on the day of screening visit or who plan to breastfeed during the trial, starting from screening visit and continuously until at least 90 days after the last immunization. women or partners who plan to become pregnant within 1 year post the screening visit. - have a known allergy, hypersensitivity, or intolerance to the planned vaccine for trial including any excipients. - used to have a history of hypersensitivity or serious reactions to vaccination. - received any vaccination within 4 weeks prior to visit 1. - don't agree to not be vaccinated during the trial, starting from screening visit and continuously until 28 days after receiving the last immunization, except emergency vaccination (e.g. rabies vaccine, tetanus vaccine). - had any medical condition (e.g., autoimmune disease) or any major surgery (e.g., requiring general anesthesia) within the past 5 years, which in the opinion of the investigator, could compromise their well-being if they participate as trial subjects in the trial, or that could prevent, limit, or confound the protocol-specified assessments. - have any surgery planned during the trial, starting from screening visit and continuously until at least 90 days after the last immunization. - had any chronic use (more than 14 continuous days) of any systemic medications that affects immune function, including immunosuppressant or other immune-modifying drugs, within 6 months prior to screening visit unless in the opinion of the investigator, the medication would not prevent, limit, or confound the protocol-specified assessments or could compromise safety of subjects. - had administration of any immunoglobulins and/or any blood products within the 3 months prior to screening visit. - had administration of another investigational product including vaccines within 60 days or 5 half-lives (whichever is longer), prior to screening visit. - with known history of aids or human immunodeficiency virus (hiv) test positive. - history of hepatitis b virus (hbv) or hepatitis c virus (hcv) infection, through medical inquiry. - history of sars, sars-cov-2 or middle east respiratory syndrome (mers) infection. suspected sars patients should be screened for sars antibodies. - previously participated in a clinical trial involving lipid nanoparticles. - are subject to exclusion periods of other clinical trials or simultaneous participation in another clinical trial. - have any affiliation with the study site (e.g., are close relative of the investigator or dependent person, such as an employee or student of the study site). - have a history of drug abuse or known medical, psychological, or social conditions within the past 5 years. in the opinion of the investigator, could comprise their well-being if they participate as trial subjects in the trial, or that could prevent, limit, or confound the protocol-specified assessments. - have a history of narcolepsy. - have history of alcohol abuse or drug addiction within 1 year prior to screening visit. - have a history of or suspected immunosuppressive condition, acquired or congenital, as determined by medical history and/or physical examination at screening visit. - have any abnormality or permanent body art (e.g., tattoo), that in the opinion of the investigator, would obstruct the ability to observe local reactions at the vaccination site. - have had any blood loss >400 ml, e.g., due to donation of blood or blood products or injury, within the 28 days prior to screening visit or plan to donate blood or plasma during the trial, starting from screening visit and continuously until at least 28 days after being given the last immunization. - travel or live in any country or region with a high sars-cov-2 infection risk (as defined at screening visit) within the 14 days prior to screening visit. - they plan to visit any country or region with a high sars-cov-2 infection risk (as defined at screening visit), from screening visit until 14 days after being given the last immunization. - symptoms of covid-19, e.g., respiratory symptoms, fever, cough, shortness of breath and breathing difficulties. - have had contact with confirmed covid-19 patients or persons tested positive for sars-cov-2 within the 30 days prior to screening visit. - are vulnerable persons, e.g., soldiers, subjects in detention, contract research organization (cro) or fosun staff or their family members. for the elderly group (age ≥65 and ≤85) - baseline laboratory abnormalities with grade ≥3 (for hematology abnormalities with grade ≥2) during screening visits, by physical examination and eligibility screening. - have had any acute illness, as determined by the investigator, with or without fever, within 72 hours prior to the prime vaccination. an acute illness which is nearly resolved with only minor residual symptoms remaining is allowable if, in the opinion of the investigator, the residual symptoms will not compromise their well-being if they participate as trial subjects in the trial, or that will not prevent, limit, or confound the protocol-specified assessments. - have a known allergy, hypersensitivity, or intolerance to the planned vaccine for trial including any excipients. - used to have a history of hypersensitivity or serious reactions to vaccination. - received any vaccination within 4 weeks prior to visit 1. - don't agree to not be vaccinated during the trial, starting from screening visit and continuously until 28 days after receiving the last immunization, except emergency vaccination (e.g. rabies vaccine, tetanus vaccine). - had administration of any immunoglobulins and/or any blood products within the 3 months prior to screening visit. - had any serious or life-threatening medical condition (e.g., autoimmune disease, cardiovascular disease) within the past 5 years, which in the opinion of the investigator, could compromise their well-being if they participate as trial subjects in the trial, or that could prevent, limit, or confound the protocol-specified assessments. - have any surgery planned during the trial, starting from screening visit and continuously until at least 90 days after the last immunization. - had any chronic use (more than 14 continuous days) of any systemic medications that affects immune function, including immunosuppressant or other immune-modifying drugs, within 6 months prior to screening visit unless in the opinion of the investigator, the medication would not prevent, limit, or confound the protocol-specified assessments or could compromise safety of subjects. - had administration of another investigational product including vaccines within 60 days or 5 half-lives (whichever is longer), prior to screening visit. - with known history of aids or hiv test positive. - history of hbv or hcv infection. - history of sars, sars-cov-2 or mers infection. suspected sars patients should be screened for sars antibodies. - previously participated in a clinical trial involving lipid nanoparticles. - are subject to exclusion periods of other clinical trials or simultaneous participation in another clinical trial. - have any affiliation with the study site (e.g., are close relative of the investigator or dependent person, such as an employee or student of the study site). - have a history of drug abuse or known medical, psychological, or social conditions within the past 5 years. in the opinion of the investigator, could comprise their well-being if they participate as trial subjects in the trial, or that could prevent, limit, or confound the protocol-specified assessments. - have a history of narcolepsy. - have history of alcohol abuse or drug addiction within 1 year prior to screening visit. - have a history of or suspected immunosuppressive condition, acquired or congenital, as determined by medical history and/or physical examination at screening visit. - have any abnormality or permanent body art (e.g., tattoo), that in the opinion of the investigator, would obstruct the ability to observe local reactions at the vaccination site. - have had any blood loss >400 ml, e.g., due to donation of blood or blood products or injury, within the 28 days prior to screening visit or plan to donate blood or plasma during the trial, starting from screening visit and continuously until at least 28 days after being given the last immunization. - travel or live in any country or region with a high sars-cov-2 infection risk (as defined at screening visit) within the 14 days prior to screening visit. - they plan to visit any country or region with a high sars-cov-2 infection risk (as defined at screening visit), from screening visit until 14 days after being given the last immunization. - symptoms of covid-19, e.g., respiratory symptoms, fever, cough, shortness of breath and breathing difficulties. - have had contact with confirmed covid-19 patients or persons tested positive for sars-cov-2 nucleic acids or antibodies within the 30 days prior to screening visit. - are vulnerable persons, e.g., soldiers, subjects in detention, cro or fosun staff or their family members.