Inclusion Criteria for Vaccination (VAC) cohort:  aged ≥ 18 years old; and have documented to have no previous COVID-19 infection; and will receive any type of COVID-19 vaccines; and agree to hand in study samples (stool and blood); and agree to sign the informed consent  Inclusion Criteria for COVID-19 convalescent (CON) cohort:  aged ≥ 18 years old; and recovered from varying severity of COVID-19; and agree to hand in study samples (stool and blood); and agree to sign the informed consent  Exclusion Criteria:  None