* have had any acute illness, as determined by the investigator, with or without fever, within 72 hours prior to the first immunization. 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 participants in the trial, or that could prevent, limit, or confound the protocol-specified assessments. * are breastfeeding on the day of visit 0 or who plan to breastfeed during the trial, starting after visit 0 and continuously until at least 90 days after receiving the last immunization. * have a known allergy, hypersensitivity, or intolerance to the planned investigational medicinal product (imp) including any excipients of the imp. * had any medical condition 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 participants in the trial, or that could prevent, limit, or confound the protocol-specified assessments. * have any surgery planned during the trial, starting after visit 0 and continuously until at least 90 days after receiving the last immunization. * had any chronic use (more than 21 continuous days) of any systemic medications, including immunosuppressants or other immune-modifying drugs, within the 6 months prior to visit 0 unless in the opinion of the investigator, the medication would not prevent, limit, or confound the protocol-specified assessments or could compromise participant safety. * received any vaccination within the 28 days prior to visit 0. * had administration of any immunoglobulins and/or any blood products within the 3 months prior to visit 0. * had administration of another imp including vaccines within 60 days or 5 half-lives (whichever is longer), prior to visit 0. * have a known history or a positive test of any of human immunodeficiency virus (hiv) 1 or 2, hepatitis b, or hepatitis c, within the 30 days prior to visit 0. * have a positive polymerase chain reaction (pcr)-based test for severe acute respiratory syndrome coronavirus 2 (sars-cov-2) within the 30 days prior to visit 1. * have a positive drugs of abuse (for amphetamines, benzodiazepines, barbiturates, cocaine, cannabinoids, opiates, methadone, methamphetamines, phencyclidine, and tricyclic antidepressants) result at visit 0 or visit 1. * have a positive breath alcohol test at visit 0 or visit 1. * previously participated in an investigational trial involving lipid nanoparticles. * are subject to exclusion periods from other investigational trials or simultaneous participation in another clinical trial. * have any affiliation with the trial site (e.g., are close relative of the investigator or dependent person, such as an employee or student of the trial site). * have a history (within the past 5 years) of substance abuse or known medical, psychological, or social conditions which, in the opinion of the investigator, could compromise their well-being if they participate as trial participants in the trial, or that could prevent, limit, or confound the protocol-specified assessments. * have a history of hypersensitivity or serious reactions to previous vaccinations. * have a history of guillain-barré syndrome within 6 weeks following a previous vaccination. * have a history of narcolepsy. * have history of alcohol abuse or drug addiction within 1 year before visit 0. * have a history of or suspected immunosuppressive condition, acquired or congenital, as determined by medical history and/or physical examination at visit 0. * 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 injection site. * have had any blood loss \>450 ml, e.g., due to donation of blood or blood products or injury, within the 7 days prior to visit 0 or plan to donate blood during the trial, starting after visit 0 and continuously until at least 7 days after receiving the last immunization. * symptoms of covid-19, e.g., respiratory symptoms, fever, cough, shortness of breath and breathing difficulties. * have had contact with persons diagnosed with covid-19 or who tested positive for sars-cov-2 by any diagnostic test within the 30 days prior to visit 1. * are soldiers, participants in detention, contract research organization (cro) or sponsor staff or their family members. * regular receipt of inhaled/nebulized corticosteroids. * have a condition known to put them at high risk for severe covid-19, including those with any of the following risk factors: * cancer * copd (chronic obstructive pulmonary disease) * immunocompromised state (weakened immune system) from solid organ transplant * obesity (bmi of 30 or higher) * serious heart conditions, such as heart failure, coronary artery disease, or cardiomyopathies * sickle cell disease * diabetes mellitus * hypertension * asthma * chronic liver disease * known stage 3 or worse chronic kidney disease (glomerular filtration rate \<60 ml/min/1.73 m\^2) * anticipating the need for immunosuppressive treatment within the next 6 months * resident in a long-term facility * current vaping or smoking (occasional smoking is acceptable) * history of chronic smoking within the prior year

* have had any acute illness, as determined by the investigator, with or without fever, within 72 hours prior to the first immunization. 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 participants in the trial, or that could prevent, limit, or confound the protocol-specified assessments. * are breastfeeding on the day of visit 0 or who plan to breastfeed during the trial, starting after visit 0 and continuously until at least 90 days after receiving the last immunization. * have a known allergy, hypersensitivity, or intolerance to the planned investigational medicinal product (imp) including any excipients of the imp. * had any medical condition 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 participants in the trial, or that could prevent, limit, or confound the protocol-specified assessments. * have any surgery planned during the trial, starting after visit 0 and continuously until at least 90 days after receiving the last immunization. * had any chronic use (more than 21 continuous days) of any systemic medications, including immunosuppressants or other immune-modifying drugs, within the 6 months prior to visit 0 unless in the opinion of the investigator, the medication would not prevent, limit, or confound the protocol-specified assessments or could compromise participant safety. * received any vaccination within the 28 days prior to visit 0. * had administration of any immunoglobulins and/or any blood products within the 3 months prior to visit 0. * had administration of another imp including vaccines within 60 days or 5 half-lives (whichever is longer), prior to visit 0. * have a known history or a positive test of any of human immunodeficiency virus (hiv) 1 or 2, hepatitis b, or hepatitis c, within the 30 days prior to visit 0. * have a positive polymerase chain reaction (pcr)-based test for severe acute respiratory syndrome coronavirus 2 (sars-cov-2) within the 30 days prior to visit 1. * have a positive drugs of abuse (for amphetamines, benzodiazepines, barbiturates, cocaine, cannabinoids, opiates, methadone, methamphetamines, phencyclidine, and tricyclic antidepressants) result at visit 0 or visit 1. * have a positive breath alcohol test at visit 0 or visit 1. * previously participated in an investigational trial involving lipid nanoparticles. * are subject to exclusion periods from other investigational trials or simultaneous participation in another clinical trial. * have any affiliation with the trial site (e.g., are close relative of the investigator or dependent person, such as an employee or student of the trial site). * have a history (within the past 5 years) of substance abuse or known medical, psychological, or social conditions which, in the opinion of the investigator, could compromise their well-being if they participate as trial participants in the trial, or that could prevent, limit, or confound the protocol-specified assessments. * have a history of hypersensitivity or serious reactions to previous vaccinations. * have a history of guillain-barré syndrome within 6 weeks following a previous vaccination. * have a history of narcolepsy. * have history of alcohol abuse or drug addiction within 1 year before visit 0. * have a history of or suspected immunosuppressive condition, acquired or congenital, as determined by medical history and/or physical examination at visit 0. * 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 injection site. * have had any blood loss \>450 ml, e.g., due to donation of blood or blood products or injury, within the 7 days prior to visit 0 or plan to donate blood during the trial, starting after visit 0 and continuously until at least 7 days after receiving the last immunization. * symptoms of covid-19, e.g., respiratory symptoms, fever, cough, shortness of breath and breathing difficulties. * have had contact with persons diagnosed with covid-19 or who tested positive for sars-cov-2 by any diagnostic test within the 30 days prior to visit 1. * are soldiers, participants in detention, contract research organization (cro) or sponsor staff or their family members. * regular receipt of inhaled/nebulized corticosteroids. * have a condition known to put them at high risk for severe covid-19, including those with any of the following risk factors: * cancer * copd (chronic obstructive pulmonary disease) * immunocompromised state (weakened immune system) from solid organ transplant * obesity (bmi of 30 or higher) * serious heart conditions, such as heart failure, coronary artery disease, or cardiomyopathies * sickle cell disease * diabetes mellitus * hypertension * asthma * chronic liver disease * known stage 3 or worse chronic kidney disease (glomerular filtration rate \<60 ml/min/1.73 m\^2) * anticipating the need for immunosuppressive treatment within the next 6 months * resident in a long-term facility * current vaping or smoking (occasional smoking is acceptable) * history of chronic smoking within the prior year

have had any acute illness, as determined by the investigator, with or without fever, within 72 hours prior to the first immunization. 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 participants in the trial, or that could prevent, limit, or confound the protocol-specified assessments. are breastfeeding on the day of visit 0 or who plan to breastfeed during the trial, starting after visit 0 and continuously until at least 90 days after receiving the last immunization. have a known allergy, hypersensitivity, or intolerance to the planned investigational medicinal product (imp) including any excipients of the imp. had any medical condition 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 participants in the trial, or that could prevent, limit, or confound the protocol-specified assessments. have any surgery planned during the trial, starting after visit 0 and continuously until at least 90 days after receiving the last immunization. had any chronic use (more than 21 continuous days) of any systemic medications, including immunosuppressants or other immune-modifying drugs, within the 6 months prior to visit 0 unless in the opinion of the investigator, the medication would not prevent, limit, or confound the protocol-specified assessments or could compromise participant safety. received any vaccination within the 28 days prior to visit 0. had administration of any immunoglobulins and/or any blood products within the 3 months prior to visit 0. had administration of another imp including vaccines within 60 days or 5 half-lives (whichever is longer), prior to visit 0. have a known history or a positive test of any of human immunodeficiency virus (hiv) 1 or 2, hepatitis b, or hepatitis c, within the 30 days prior to visit 0. have a positive polymerase chain reaction (pcr)-based test for severe acute respiratory syndrome coronavirus 2 (sars-cov-2) within the 30 days prior to visit 1. have a positive drugs of abuse (for amphetamines, benzodiazepines, barbiturates, cocaine, cannabinoids, opiates, methadone, methamphetamines, phencyclidine, and tricyclic antidepressants) result at visit 0 or visit 1. have a positive breath alcohol test at visit 0 or visit 1. previously participated in an investigational trial involving lipid nanoparticles. are subject to exclusion periods from other investigational trials or simultaneous participation in another clinical trial. have any affiliation with the trial site (e.g., are close relative of the investigator or dependent person, such as an employee or student of the trial site). have a history (within the past 5 years) of substance abuse or known medical, psychological, or social conditions which, in the opinion of the investigator, could compromise their well-being if they participate as trial participants in the trial, or that could prevent, limit, or confound the protocol-specified assessments. have a history of hypersensitivity or serious reactions to previous vaccinations. have a history of guillain-barré syndrome within 6 weeks following a previous vaccination. have a history of narcolepsy. have history of alcohol abuse or drug addiction within 1 year before visit 0. have a history of or suspected immunosuppressive condition, acquired or congenital, as determined by medical history and/or physical examination at visit 0. 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 injection site. have had any blood loss >450 ml, e.g., due to donation of blood or blood products or injury, within the 7 days prior to visit 0 or plan to donate blood during the trial, starting after visit 0 and continuously until at least 7 days after receiving the last immunization. symptoms of covid-19, e.g., respiratory symptoms, fever, cough, shortness of breath and breathing difficulties. have had contact with persons diagnosed with covid-19 or who tested positive for sars-cov-2 by any diagnostic test within the 30 days prior to visit 1. are soldiers, participants in detention, contract research organization (cro) or sponsor staff or their family members. regular receipt of inhaled/nebulized corticosteroids. have a condition known to put them at high risk for severe covid-19, including those with any of the following risk factors: cancer copd (chronic obstructive pulmonary disease) immunocompromised state (weakened immune system) from solid organ transplant obesity (bmi of 30 or higher) serious heart conditions, such as heart failure, coronary artery disease, or cardiomyopathies sickle cell disease diabetes mellitus hypertension asthma chronic liver disease known stage 3 or worse chronic kidney disease (glomerular filtration rate <60 ml/min/1.73 m^2) anticipating the need for immunosuppressive treatment within the next 6 months resident in a long-term facility current vaping or smoking (occasional smoking is acceptable) history of chronic smoking within the prior year

have had any acute illness, as determined by the investigator, with or without fever, within 72 hours prior to the first immunization. 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 participants in the trial, or that could prevent, limit, or confound the protocol-specified assessments. are breastfeeding on the day of visit 0 or who plan to breastfeed during the trial, starting after visit 0 and continuously until at least 90 days after receiving the last immunization. have a known allergy, hypersensitivity, or intolerance to the planned investigational medicinal product (imp) including any excipients of the imp. had any medical condition 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 participants in the trial, or that could prevent, limit, or confound the protocol-specified assessments. have any surgery planned during the trial, starting after visit 0 and continuously until at least 90 days after receiving the last immunization. had any chronic use (more than 21 continuous days) of any systemic medications, including immunosuppressants or other immune-modifying drugs, within the 6 months prior to visit 0 unless in the opinion of the investigator, the medication would not prevent, limit, or confound the protocol-specified assessments or could compromise participant safety. received any vaccination within the 28 days prior to visit 0. had administration of any immunoglobulins and/or any blood products within the 3 months prior to visit 0. had administration of another imp including vaccines within 60 days or 5 half-lives (whichever is longer), prior to visit 0. have a known history or a positive test of any of human immunodeficiency virus (hiv) 1 or 2, hepatitis b, or hepatitis c, within the 30 days prior to visit 0. have a positive polymerase chain reaction (pcr)-based test for severe acute respiratory syndrome coronavirus 2 (sars-cov-2) within the 30 days prior to visit 1. have a positive drugs of abuse (for amphetamines, benzodiazepines, barbiturates, cocaine, cannabinoids, opiates, methadone, methamphetamines, phencyclidine, and tricyclic antidepressants) result at visit 0 or visit 1. have a positive breath alcohol test at visit 0 or visit 1. previously participated in an investigational trial involving lipid nanoparticles. are subject to exclusion periods from other investigational trials or simultaneous participation in another clinical trial. have any affiliation with the trial site (e.g., are close relative of the investigator or dependent person, such as an employee or student of the trial site). have a history (within the past 5 years) of substance abuse or known medical, psychological, or social conditions which, in the opinion of the investigator, could compromise their well-being if they participate as trial participants in the trial, or that could prevent, limit, or confound the protocol-specified assessments. have a history of hypersensitivity or serious reactions to previous vaccinations. have a history of guillain-barré syndrome within 6 weeks following a previous vaccination. have a history of narcolepsy. have history of alcohol abuse or drug addiction within 1 year before visit 0. have a history of or suspected immunosuppressive condition, acquired or congenital, as determined by medical history and/or physical examination at visit 0. 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 injection site. have had any blood loss >450 ml, e.g., due to donation of blood or blood products or injury, within the 7 days prior to visit 0 or plan to donate blood during the trial, starting after visit 0 and continuously until at least 7 days after receiving the last immunization. symptoms of covid-19, e.g., respiratory symptoms, fever, cough, shortness of breath and breathing difficulties. have had contact with persons diagnosed with covid-19 or who tested positive for sars-cov-2 by any diagnostic test within the 30 days prior to visit 1. are soldiers, participants in detention, contract research organization (cro) or sponsor staff or their family members. regular receipt of inhaled/nebulized corticosteroids. have a condition known to put them at high risk for severe covid-19, including those with any of the following risk factors: cancer copd (chronic obstructive pulmonary disease) immunocompromised state (weakened immune system) from solid organ transplant obesity (bmi of 30 or higher) serious heart conditions, such as heart failure, coronary artery disease, or cardiomyopathies sickle cell disease diabetes mellitus hypertension asthma chronic liver disease known stage 3 or worse chronic kidney disease (glomerular filtration rate <60 ml/min/1.73 m^2) anticipating the need for immunosuppressive treatment within the next 6 months resident in a long-term facility current vaping or smoking (occasional smoking is acceptable) history of chronic smoking within the prior year

- have had any acute illness, as determined by the investigator, with or without fever, within 72 hours prior to the first immunization. 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 visit 0 or who plan to breastfeed during the trial, starting after visit 0 and continuously until at least 90 days after receiving the last immunization. - have a known allergy, hypersensitivity, or intolerance to the planned investigational medicinal product (imp) including any excipients of the imp. - had any medical condition 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 after visit 0 and continuously until at least 90 days after receiving the last immunization. - had any chronic use (more than 21 continuous days) of any systemic medications, including immunosuppressants or other immune-modifying drugs, within the 6 months prior to visit 0 unless in the opinion of the investigator, the medication would not prevent, limit, or confound the protocol-specified assessments or could compromise subject safety. - received any vaccination within the 28 days prior to visit 0. - had administration of any immunoglobulins and/or any blood products within the 3 months prior to visit 0. - had administration of another imp including vaccines within 60 days or 5 half-lives (whichever is longer), prior to visit 0. - have a known history or a positive test of any of human immunodeficiency virus (hiv) 1 or 2, hepatitis b, or hepatitis c, within the 30 days prior to visit 0. - have a positive polymerase chain reaction (pcr)-based test for severe acute respiratory syndrome coronavirus 2 (sars-cov-2) within the 30 days prior to visit 1. - have a positive drugs of abuse (for amphetamines, benzodiazepines, barbiturates, cocaine, cannabinoids, opiates, methadone, methamphetamines, phencyclidine, and tricyclic antidepressants) result at visit 0 or visit 1. - have a positive breath alcohol test at visit 0 or visit 1. - previously participated in an investigational trial involving lipid nanoparticles. - are subject to exclusion periods from other investigational trials or simultaneous participation in another clinical trial. - have any affiliation with the trial site (e.g., are close relative of the investigator or dependent person, such as an employee or student of the trial site). - have a history (within the past 5 years) of substance abuse or known medical, psychological, or social conditions 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 a history of hypersensitivity or serious reactions to previous vaccinations. - have a history of guillain-barré syndrome within 6 weeks following a previous vaccination. - have a history of narcolepsy. - have history of alcohol abuse or drug addiction within 1 year before visit 0. - have a history of or suspected immunosuppressive condition, acquired or congenital, as determined by medical history and/or physical examination at visit 0. - 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 injection site. - have had any blood loss >450 ml, e.g., due to donation of blood or blood products or injury, within the 7 days prior to visit 0 or plan to donate blood during the trial, starting after visit 0 and continuously until at least 7 days after receiving the last immunization. - symptoms of covid-19, e.g., respiratory symptoms, fever, cough, shortness of breath and breathing difficulties. - have had contact with persons diagnosed with covid-19 or who tested positive for sars-cov-2 by any diagnostic test within the 30 days prior to visit 1. - are soldiers, subjects in detention, contract research organization (cro) or sponsor staff or their family members. - regular receipt of inhaled/nebulized corticosteroids. - have a condition known to put them at high risk for severe covid-19, including those with any of the following risk factors: - cancer - copd (chronic obstructive pulmonary disease) - immunocompromised state (weakened immune system) from solid organ transplant - obesity (bmi of 30 or higher) - serious heart conditions, such as heart failure, coronary artery disease, or cardiomyopathies - sickle cell disease - diabetes mellitus - hypertension - asthma - chronic liver disease - known stage 3 or worse chronic kidney disease (glomerular filtration rate <60 ml/min/1.73 m^2) - anticipating the need for immunosuppressive treatment within the next 6 months - resident in a long-term facility - current vaping or smoking (occasional smoking is acceptable) - history of chronic smoking within the prior year

- have had any acute illness, as determined by the investigator, with or without fever, within 72 hours prior to the first immunization. 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 visit 0 or who plan to breastfeed during the trial, starting after visit 0 and continuously until at least 90 days after receiving the last immunization. - have a known allergy, hypersensitivity, or intolerance to the planned investigational medicinal product (imp) including any excipients of the imp. - had any medical condition 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 after visit 0 and continuously until at least 90 days after receiving the last immunization. - had any chronic use (more than 21 continuous days) of any systemic medications, including immunosuppressants or other immune-modifying drugs, within the 6 months prior to visit 0 unless in the opinion of the investigator, the medication would not prevent, limit, or confound the protocol-specified assessments or could compromise subject safety. - received any vaccination within the 28 days prior to visit 0. - had administration of any immunoglobulins and/or any blood products within the 3 months prior to visit 0. - had administration of another imp including vaccines within 60 days or 5 half-lives (whichever is longer), prior to visit 0. - have a known history or a positive test of any of human immunodeficiency virus (hiv) 1 or 2, hepatitis b, or hepatitis c, within the 30 days prior to visit 0. - have a positive polymerase chain reaction (pcr)-based test for severe acute respiratory syndrome coronavirus 2 (sars-cov-2) within the 30 days prior to visit 1. - have a positive drugs of abuse (for amphetamines, benzodiazepines, barbiturates, cocaine, cannabinoids, opiates, methadone, methamphetamines, phencyclidine, and tricyclic antidepressants) result at visit 0 or visit 1. - have a positive breath alcohol test at visit 0 or visit 1. - previously participated in an investigational trial involving lipid nanoparticles. - are subject to exclusion periods from other investigational trials or simultaneous participation in another clinical trial. - have any affiliation with the trial site (e.g., are close relative of the investigator or dependent person, such as an employee or student of the trial site). - have a history (within the past 5 years) of substance abuse or known medical, psychological, or social conditions 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 a history of hypersensitivity or serious reactions to previous vaccinations. - have a history of guillain-barré syndrome within 6 weeks following a previous vaccination. - have a history of narcolepsy. - have history of alcohol abuse or drug addiction within 1 year before visit 0. - have a history of or suspected immunosuppressive condition, acquired or congenital, as determined by medical history and/or physical examination at visit 0. - 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 injection site. - have had any blood loss >450 ml, e.g., due to donation of blood or blood products or injury, within the 7 days prior to visit 0 or plan to donate blood during the trial, starting after visit 0 and continuously until at least 7 days after receiving the last immunization. - symptoms of covid-19, e.g., respiratory symptoms, fever, cough, shortness of breath and breathing difficulties. - have had contact with persons diagnosed with covid-19 or who tested positive for sars-cov-2 by any diagnostic test within the 30 days prior to visit 1. - are soldiers, subjects in detention, contract research organization (cro) or sponsor staff or their family members. - regular receipt of inhaled/nebulized corticosteroids. - have a condition known to put them at high risk for severe covid-19, including those with any of the following risk factors: - cancer - copd (chronic obstructive pulmonary disease) - immunocompromised state (weakened immune system) from solid organ transplant - obesity (bmi of 30 or higher) - serious heart conditions, such as heart failure, coronary artery disease, or cardiomyopathies - sickle cell disease - diabetes mellitus - hypertension - asthma - chronic liver disease - known stage 3 or worse chronic kidney disease (glomerular filtration rate <60 ml/min/1.73 m^2) - anticipating the need for immunosuppressive treatment within the next 6 months - resident in a long-term facility - current vaping or smoking (occasional smoking is acceptable) - history of chronic smoking within the prior year

- have had any acute illness, as determined by the investigator, with or without fever, within 72 hours prior to the first immunization. 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 visit 0 or who plan to breastfeed during the trial, starting after visit 0 and continuously until at least 90 days after receiving the last immunization. - have a known allergy, hypersensitivity, or intolerance to the planned investigational medicinal product (imp) including any excipients of the imp. - had any medical condition 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 after visit 0 and continuously until at least 90 days after receiving the last immunization. - had any chronic use (more than 21 continuous days) of any systemic medications, including immunosuppressants or other immune-modifying drugs, within the 6 months prior to visit 0 unless in the opinion of the investigator, the medication would not prevent, limit, or confound the protocol-specified assessments or could compromise subject safety. - received any vaccination within the 28 days prior to visit 0. - had administration of any immunoglobulins and/or any blood products within the 3 months prior to visit 0. - had administration of another imp including vaccines within 60 days or 5 half-lives (whichever is longer), prior to visit 0. - have a known history or a positive test of any of human immunodeficiency virus (hiv) 1 or 2, hepatitis b, or hepatitis c, within the 30 days prior to visit 0. - have a positive polymerase chain reaction (pcr)-based test for severe acute respiratory syndrome coronavirus 2 (sars-cov-2) within the 30 days prior to visit 1. - have a positive drugs of abuse (for amphetamines, benzodiazepines, barbiturates, cocaine, cannabinoids, opiates, methadone, methamphetamines, phencyclidine, and tricyclic antidepressants) result at visit 0 or visit 1. - have a positive breath alcohol test at visit 0 or visit 1. - previously participated in an investigational trial involving lipid nanoparticles. - are subject to exclusion periods from other investigational trials or simultaneous participation in another clinical trial. - have any affiliation with the trial site (e.g., are close relative of the investigator or dependent person, such as an employee or student of the trial site). - have a history (within the past 5 years) of substance abuse or known medical, psychological, or social conditions 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 a history of hypersensitivity or serious reactions to previous vaccinations. - have a history of guillain-barré syndrome within 6 weeks following a previous vaccination. - have a history of narcolepsy. - have history of alcohol abuse or drug addiction within 1 year before visit 0. - have a history of or suspected immunosuppressive condition, acquired or congenital, as determined by medical history and/or physical examination at visit 0. - 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 injection site. - have had any blood loss >450 ml, e.g., due to donation of blood or blood products or injury, within the 7 days prior to visit 0 or plan to donate blood during the trial, starting after visit 0 and continuously until at least 7 days after receiving the last immunization. - symptoms of covid-19, e.g., respiratory symptoms, fever, cough, shortness of breath and breathing difficulties. - have had contact with persons diagnosed with covid-19 or who tested positive for sars-cov-2 by any diagnostic test within the 30 days prior to visit 1. - are soldiers, subjects in detention, contract research organization (cro) or sponsor staff or their family members. - regular receipt of inhaled/nebulized corticosteroids. - for older adults only: have a condition known to put them at high risk for severe covid-19, including those with any of the following risk factors: - hypertension - diabetes mellitus - chronic pulmonary disease - asthma - chronic liver disease - known stage 3 or worse chronic kidney disease (glomerular filtration rate <60 ml/min/1.73 m^2) - anticipating the need for immunosuppressive treatment within the next 6 months - resident in a long-term facility - current vaping or smoking (occasional smoking is acceptable) - history of chronic smoking within the prior year

- have had any acute illness, as determined by the investigator, with or without fever, within 72 hours prior to the first immunization. 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 visit 0 or who plan to breastfeed during the trial, starting after visit 0 and continuously until at least 90 days after receiving the last immunization. - have a known allergy, hypersensitivity, or intolerance to the planned investigational medicinal product (imp) including any excipients of the imp. - had any medical condition 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 after visit 0 and continuously until at least 90 days after receiving the last immunization. - had any chronic use (more than 21 continuous days) of any systemic medications, including immunosuppressants or other immune-modifying drugs, within the 6 months prior to visit 0 unless in the opinion of the investigator, the medication would not prevent, limit, or confound the protocol-specified assessments or could compromise subject safety. - received any vaccination within the 28 days prior to visit 0. - had administration of any immunoglobulins and/or any blood products within the 3 months prior to visit 0. - had administration of another imp including vaccines within 60 days or 5 half-lives (whichever is longer), prior to visit 0. - have a known history or a positive test of any of human immunodeficiency virus (hiv) 1 or 2, hepatitis b, or hepatitis c, within the 30 days prior to visit 0. - have a positive polymerase chain reaction (pcr)-based test for severe acute respiratory syndrome coronavirus 2 (sars-cov-2) within the 30 days prior to visit 1. - have a positive drugs of abuse (for amphetamines, benzodiazepines, barbiturates, cocaine, cannabinoids, opiates, methadone, methamphetamines, phencyclidine, and tricyclic antidepressants) result at visit 0 or visit 1. - have a positive breath alcohol test at visit 0 or visit 1. - previously participated in an investigational trial involving lipid nanoparticles. - are subject to exclusion periods from other investigational trials or simultaneous participation in another clinical trial. - have any affiliation with the trial site (e.g., are close relative of the investigator or dependent person, such as an employee or student of the trial site). - have a history (within the past 5 years) of substance abuse or known medical, psychological, or social conditions 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 a history of hypersensitivity or serious reactions to previous vaccinations. - have a history of guillain-barré syndrome within 6 weeks following a previous vaccination. - have a history of narcolepsy. - have history of alcohol abuse or drug addiction within 1 year before visit 0. - have a history of or suspected immunosuppressive condition, acquired or congenital, as determined by medical history and/or physical examination at visit 0. - 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 injection site. - have had any blood loss >450 ml, e.g., due to donation of blood or blood products or injury, within the 7 days prior to visit 0 or plan to donate blood during the trial, starting after visit 0 and continuously until at least 7 days after receiving the last immunization. - symptoms of covid-19, e.g., respiratory symptoms, fever, cough, shortness of breath and breathing difficulties. - have had contact with persons diagnosed with covid-19 or who tested positive for sars-cov-2 by any diagnostic test within the 30 days prior to visit 1. - are soldiers, subjects in detention, contract research organization (cro) or sponsor staff or their family members. - regular receipt of inhaled/nebulized corticosteroids. - for older adults only: have a condition known to put them at high risk for severe covid-19, including those with any of the following risk factors: - hypertension - diabetes mellitus - chronic pulmonary disease - asthma - chronic liver disease - known stage 3 or worse chronic kidney disease (glomerular filtration rate <60 ml/min/1.73 m^2) - anticipating the need for immunosuppressive treatment within the next 6 months - resident in a long-term facility - current vaping or smoking (occasional smoking is acceptable) - history of chronic smoking within the prior year