inclusion criteria: 1. male or female participant ≥ 65 years of age at randomization. 2. healthy adults or adults with pre-existing medical conditions who are in stable condition. a stable medical condition is defined as disease not requiring significant change in therapy or hospitalization for worsening disease 3 months before enrollment and expected to remain stable for the duration of the study. 3. participant is willing and able to comply with all required study visits and follow-up required by this protocol. 4. participant has not travelled overseas within 14 days of screening and will not have any oversea traveling throughout the study period. 5. participant is able to understand and comply with study requirements/procedures (if applicable, with assistance by caregiver, surrogate, or legally authorized representative) based on the assessment of the investigator and must provide written informed consent.

inclusion criteria: 1. male or female participant ≥ 65 years of age at randomization. 2. healthy adults or adults with pre-existing medical conditions who are in stable condition. a stable medical condition is defined as disease not requiring significant change in therapy or hospitalization for worsening disease 3 months before enrollment and expected to remain stable for the duration of the study. 3. participant is willing and able to comply with all required study visits and follow-up required by this protocol. 4. participant has not travelled overseas within 14 days of screening and will not have any oversea traveling throughout the study period. 5. participant is able to understand and comply with study requirements/procedures (if applicable, with assistance by caregiver, surrogate, or legally authorized representative) based on the assessment of the investigator and must provide written informed consent.

inclusion criteria: male or female participant ≥ 65 years of age at randomization. healthy adults or adults with pre-existing medical conditions who are in stable condition. a stable medical condition is defined as disease not requiring significant change in therapy or hospitalization for worsening disease 3 months before enrollment and expected to remain stable for the duration of the study. participant is willing and able to comply with all required study visits and follow-up required by this protocol. participant has not travelled overseas within 14 days of screening and will not have any oversea traveling throughout the study period. participant is able to understand and comply with study requirements/procedures (if applicable, with assistance by caregiver, surrogate, or legally authorized representative) based on the assessment of the investigator and must provide written informed consent.

inclusion criteria: male or female participant ≥ 65 years of age at randomization. healthy adults or adults with pre-existing medical conditions who are in stable condition. a stable medical condition is defined as disease not requiring significant change in therapy or hospitalization for worsening disease 3 months before enrollment and expected to remain stable for the duration of the study. participant is willing and able to comply with all required study visits and follow-up required by this protocol. participant has not travelled overseas within 14 days of screening and will not have any oversea traveling throughout the study period. participant is able to understand and comply with study requirements/procedures (if applicable, with assistance by caregiver, surrogate, or legally authorized representative) based on the assessment of the investigator and must provide written informed consent.

inclusion criteria: 1. male or female participant ≥ 65 years of age at randomization. 2. healthy adults or adults with pre-existing medical conditions who are in stable condition. a stable medical condition is defined as disease not requiring significant change in therapy or hospitalization for worsening disease 3 months before enrollment and expected to remain stable for the duration of the study. 3. participant is willing and able to comply with all required study visits and follow-up required by this protocol. 4. participant has not travelled overseas within 14 days of screening and will not have any oversea traveling throughout the study period. 5. participant is able to understand and comply with study requirements/procedures (if applicable, with assistance by caregiver, surrogate, or legally authorized representative) based on the assessment of the investigator and must provide written informed consent.

inclusion criteria: 1. male or female participant ≥ 65 years of age at randomization. 2. healthy adults or adults with pre-existing medical conditions who are in stable condition. a stable medical condition is defined as disease not requiring significant change in therapy or hospitalization for worsening disease 3 months before enrollment and expected to remain stable for the duration of the study. 3. participant is willing and able to comply with all required study visits and follow-up required by this protocol. 4. participant has not travelled overseas within 14 days of screening and will not have any oversea traveling throughout the study period. 5. participant is able to understand and comply with study requirements/procedures (if applicable, with assistance by caregiver, surrogate, or legally authorized representative) based on the assessment of the investigator and must provide written informed consent.