Having or being vulnerable to a virus isn't a protected class.

People with disabilities are in a protected class. Being immunocompromised qualifies as a disability.

Here's a brief definition, from a government site about equal employment:

https://www.eeoc.gov/disability-discrimination#definition

It doesn't seem like immunocompromise generally constitutes a disability by that definition, without satisfying some other criteria. But I'm not a lawyer, so what do I know.

The text of the law makes it more explicit: "[...] a major life activity also includes the operation of a major bodily function, including but not limited to, functions of the immune system [...]"

https://www.law.cornell.edu/uscode/text/42/12102