1. Today the CDC issued new guidance on opening K-12 schools during the pandemic. The guidelines are more explicit and clearer than previous iterations.

They also align closely with my understanding of what is prudent at this stage of the pandemic.

https://www.cdc.gov/coronavirus/2019-ncov/downloads/community/schools-childcare/K-12-Operational-Strategy-2021-2-12.pdf

2. @apoorva_nyc, @katetaylornyt, and @DanaGoldstein have a detailed story here: https://www.nytimes.com/2021/02/12/health/school-reopenings-cdc.html

3. The CDC document notes that — unsurprisingly — community transmission level is an extremely important in determining the safety of school reopening, and throughout the document, recommendations are keyed to the underlying levels of community transmission.

4. Transmission is measured in two ways: new cases per 100,000 in the past 7 days, and test positivity rate over the past 7 days.

5. Notice that compared to past CDC guidelines, we now have four risk levels instead of five, and the indicators now refer to cases in the past 7 days instead of the past 14 days. https://www.cdc.gov/media/releases/2020/p0915-dynamic-school-decision-making-infographic.html

6. To hold the thresholds constant, all of the case counts should be halved. So, we see that the two low risk categories have been merged for the new table. The high-risk bar remains in the same place: 100 cases per 100000 per 7 days is akin to 200 cases per 100000 per 14 days.

7. But look at the moderate risk category. We've gone from <50 cases per 14 days to <50 case per 7 days. Risk levels can double from moderate risk in Sept and still remain in the moderate actegory.

This is a bit of a goalpost move, though I largely concur with the conclusions.

8. Back to the role of community transmission. The CDC's focus on this is consistent with our own modeling work. Keeping transmission down in the community is the best way to keep it down in the schools. Figure from v.1 of our paper at https://www.medrxiv.org/content/10.1101/2021.01.22.21250282v2

9. The other thing to keep in mind is right now, almost the entire country is in the CDC's red zone. Via @bhrenton: https://twitter.com/bhrenton/status/1360326688404553729

10. This underscores the importance of one of the stronger messages in the CDC guidelines:

“At any level of community transmission, all schools can provide in-person instruction (either full or hybrid), through strict adherence to mitigation strategies.”

To be continued....

(Reply to the above; I'll delete this when I continue.)