[LurkingPenguin]

When you get infected (or vaccinated), your body produces antibodies as part of its primary response. The antibody tests that are commonly done for COVID look for these already circulating antibodies.

Upon infection or vaccination, your body will also produce antibody-producing memory cells to help respond more quickly if you are infected in the future. If you want to test for these memory cells, you can't use antibody tests. You have to use specialized tests that look specifically for the memory cell responses.

There are some commercially available tests, such as https://www.t-detect.com/, which looks at the T cell response.

A lot of the commercially available antibody tests will fail to detect a prior infection after just a few months. T-Detect now says that its test can pick up infections that occurred 10 months ago. 10 months is probably not the limit of detection; it's just based on the amount of time T-Detect has been available to the public.

Researchers have found memory T cells that respond to the original SARS-CoV virus 17 years post-infection:

https://www.nature.com/articles/s41586-020-2550-z

[tzs]

Can any tests distinguish between having a response due to prior infection from having a response due to vaccination?

In the months before I was vaccinated I had on two or three occasions something that felt a bit different from the usual cold/flu/allergies that I get, but was not severe enough to justify trying to get a COVID test. I'm curious if I actually have had COVID or not.