Inclusion Criteria:  Participant must be healthy (in the physician's clinical judgment and as confirmed by medical records, and physical examination at screening). Willing to give informed consent, and answer short questionnaires on past exposure to COVID-19 and post-vaccination reactogenicity. Willing to comply with the requirements of the protocol.  Exclusion Criteria:  Participant shows signs of an acute illness (excluding minor illnesses such as diarrhea or mild upper respiratory tract infection). Participant has a positive laboratory-confirmed test result for SARS-CoV-2 infection at screening. Deemed by investigators to be unlikely to complete study protocol.