PCR testing is notorious for giving false positives when the cycle threshold is too high, so I wouldn't be surprised if it gave inaccurate results after a shot. I'm not exactly sure how the rapid antigen tests work, but they are supposed to detect protein fragments so the spike proteins might be enough to do that.
That's actually a good point, I've never heard whether spike protein by itself will or will not cause a positive test.
Like did they design the test to measure spike protein rather than other parts of the virus? That would be really insidious if so.
PCR testing is notorious for giving false positives when the cycle threshold is too high, so I wouldn't be surprised if it gave inaccurate results after a shot. I'm not exactly sure how the rapid antigen tests work, but they are supposed to detect protein fragments so the spike proteins might be enough to do that.