Inclusion Criteria:

- Lives in the continental United States (US).

- Speaks, reads, and understands English.

- Is willing and able to submit vaccination card photo(s) or vaccination records.

- Is willing and able to self-collect capillary blood during the study period via an
at-home whole-blood collection device.

- Is fully vaccinated against COVID-19 per protocol specified criteria.

Exclusion Criteria:

- Has been diagnosed with significant cognitive impairment or dementia.

- Is pregnant or planning to become pregnant during the study period.

- Primary mailing address is a Post Office box, Army Post Office, Fleet Post Office, or
Diplomatic Post Office address.

- Currently lives in a US military base located overseas, or US territories (Puerto
Rico, US Virgin Islands, Guam, Northern Mariana Island, or American Samoa).

- Is currently participating in a COVID-19 vaccine clinical trial.

- Is currently receiving chemotherapy or has received chemotherapy in the past 6 months.

- Is currently taking steroids, such as prednisone, for any condition.

- Has been diagnosed with and taking immunosuppressants for rheumatoid arthritis, lupus
or multiple sclerosis.

- Has received an organ transplant.

- Is currently undergoing dialysis of any kind (for example, hemodialysis or chronic
ambulatory dialysis) for kidney disease.