Part of the problem with serological testing is false positives. I'm no expert, but my understanding is that the tests available may have false positive rates on the order of 0.5% to 2%
If only 1% are infected, and the false positive rate is 1%, it's quite hard to determine what the test result actually means. On the other hand, some places like New York City are already at 0.7% per-capita known positives, and they're not even able to test everyone with symptoms. Their true infection rate could very well be 10%, which serological testing could confirm.
Yes, which is why a better serological test would be extremely useful, the sooner the better. In no way does this undermine the value of BillionToOne’s test, but it is irresponsible for their CEO to be saying that serological tests are not useful yet when they are.
If only 1% are infected, and the false positive rate is 1%, it's quite hard to determine what the test result actually means. On the other hand, some places like New York City are already at 0.7% per-capita known positives, and they're not even able to test everyone with symptoms. Their true infection rate could very well be 10%, which serological testing could confirm.