To be clear, I'm not saying contact tracing is useless. I'm saying its effectiveness scales inversely with the case rate. At very low case rates, the overhead

To be clear, I'm not saying contact tracing is useless. I'm saying its effectiveness scales inversely with the case rate. At very low case rates, the overhead and required adoption rates for an app-based tracing system are major disadvantages against human contact tracers. As case rates go up, that overhead starts to pay off and apps make sense. But as case rates continue to go up further, you get less and less information from contact tracing. At some point, when case rates are high enough, it basically becomes a single bit of information: did you go out? Yes? Then you were probably exposed. At that point, the app isn't adding much value! I believe that in many places around the world dealing with COVID-19, we are closer to the latter scenario than a lot of people think. No, we're not literally in the scenario above (it was an exemplar), but the general point that case rates may be too high for contact tracing to "save us" is still worth making.