Welcome to the medical surveillance state.

...the U.S. government has secretly been tracking those who didn’t get the COVID jab, or are only partially jabbed, through a previously unknown surveillance program designed by the U.S. National Center for Health Statistics (NCHS), a division of the Centers for Disease Control and Prevention (CDC)

The program was implemented on April 1, 2022, but didn’t become universally adopted by most medical clinics and hospitals across the United States until January 2023.

"Under this program, doctors at clinics and hospitals have been instructed to ask patients about their vaccination status, which is then added to their electronic medical records as a diagnostic code, known as ICD-10 code, without their knowledge or consent so that they can be tracked—not just within the health care system but outside of it as well.

https://www.theepochtimes.com/health/the-federal-government-is-tracking-the-unvaccinated_5056313.html

By "partially jabbed" is meant anyone who is not current on any recommended vaccine.

For example, ICD-10 code Z28.310 identifies those who have not received a COVID jab and Z28.311 identifies those who are not up to date on their shots. [emphasis mine]