While I ultimately disagree with the change in isolation guidance, I commiserate with the CDC's predicament. We simply don't have the testing infrastructure to do what would be optimal on risk. Frankly I'm not sure any place does at this point as Omicron spreads so rapidly. The UK had a lot of testing capacity and even they are reaching their testing limits with Omicron.
We've been making trade-offs on isolation guidance from the start of the pandemic. The data suggests even 10 day isolation has some risk (~5%) of releasing actively infectious people out of isolation. However, the longer the isolation period the higher the costs carried by people that are no longer infectious as the majority of people stop being infectious after a few days.
The unspoken part of the isolation guidance is that frankly case ascertainment has been lousy throughout this pandemic. At our best I think we got down to 1:2 to 1:3 case ascertainment for a brief period this pandemic. But for most of the pandemic we've been more like 1:4 or worse case ascertainment. Now I think we are more like 1:10 or worse during the peak of this Omicron surge.
So I do think in some respects the overall impact of different isolation guidance lengths on the trajectory of transmission is overstated this Omicron wave. If case ascertainment is 1:10 then we are talking about the risk of ~3% of active infections from shortening isolation to 5 days (~30% of people are estimated to be still infectious at 5 days). The risk is even lower than that in reality as only about ~30% of people do the full 10-day isolation period anyways.
Clearly for the most part this Omicron wave is beyond the limits of our testing and isolation.
The CDC should have been more transparent about that, mainly to speak about individual risk of leaving isolation early. But I think there are no good options with this Omicron wave without significantly more testing infrastructure.