> I'm surprised we don't see Covid mutations that invalidate PCR tests The people who design the tests know which parts of the sequence are more likely to mut

> I'm surprised we don't see Covid mutations that invalidate PCR tests The people who design the tests know which parts of the sequence are more likely to mutate, so they pick the more conserved parts. Also, most PCR tests check for 3 different parts of the sequence. Which is why Omicron can still be detected even if there is a mutation in one part checked by the test, since the other 2 parts still match (the so called S-gene-dropout).