Serology tests are a thing for a lot of vaccines. You can get them from a doctor if you are traveling overseas to see if you need redo a vaccine.

I'm not a doctor, but if you don't have any kind of immune response after 2 doses of pfizer/moderna. I'd strongly suggest that you ask about a serology/antibody test especially if you are older or have health conditions.

https://www.cdc.gov/coronavirus/2019-ncov/lab/serology-testi...