substudy a inclusion criteria: 1. male or female participants ≥65 years of age at visit 1 (day 1). 2. participants who are willing and able to comply with all scheduled visits, investigational plan, laboratory tests, lifestyle considerations, and other study procedures. 3. healthy participants who are determined by medical history, physical examination (if required), and clinical judgment of the investigator to be eligible for inclusion in the study. 4. capable of giving signed informed consent as described in the protocol, which includes compliance with the requirements and restrictions listed in the icd and in this protocol. 5. participants who have received at least 3 prior us authorized mrna covid 19 vaccines, with the last dose being an updated (bivalent) vaccine given at least ≥150 days before visit a101 (day 1). substudy a

substudy a inclusion criteria: 1. male or female participants ≥65 years of age at visit 1 (day 1). 2. participants who are willing and able to comply with all scheduled visits, investigational plan, laboratory tests, lifestyle considerations, and other study procedures. 3. healthy participants who are determined by medical history, physical examination (if required), and clinical judgment of the investigator to be eligible for inclusion in the study. 4. capable of giving signed informed consent as described in the protocol, which includes compliance with the requirements and restrictions listed in the icd and in this protocol. 5. participants who have received at least 3 prior us authorized mrna covid 19 vaccines, with the last dose being an updated (bivalent) vaccine given at least ≥150 days before visit a101 (day 1). substudy a

substudy a inclusion criteria: male or female participants ≥65 years of age at visit 1 (day 1). participants who are willing and able to comply with all scheduled visits, investigational plan, laboratory tests, lifestyle considerations, and other study procedures. healthy participants who are determined by medical history, physical examination (if required), and clinical judgment of the investigator to be eligible for inclusion in the study. capable of giving signed informed consent as described in the protocol, which includes compliance with the requirements and restrictions listed in the icd and in this protocol. participants who have received at least 3 prior us authorized mrna covid 19 vaccines, with the last dose being an updated (bivalent) vaccine given at least ≥150 days before visit a101 (day 1). substudy a

substudy a inclusion criteria: male or female participants ≥65 years of age at visit 1 (day 1). participants who are willing and able to comply with all scheduled visits, investigational plan, laboratory tests, lifestyle considerations, and other study procedures. healthy participants who are determined by medical history, physical examination (if required), and clinical judgment of the investigator to be eligible for inclusion in the study. capable of giving signed informed consent as described in the protocol, which includes compliance with the requirements and restrictions listed in the icd and in this protocol. participants who have received at least 3 prior us authorized mrna covid 19 vaccines, with the last dose being an updated (bivalent) vaccine given at least ≥150 days before visit a101 (day 1). substudy a