I think that’s right. Although the data still can tell us something after we get into that ambiguous range where it’s hard to distinguish increasing covid and decreasing flu.
One nice thing about this pattern is that it provides some evidence that the anti-covid interventions are reducing the spread of fever-inducing diseases. And the size of the drop in total fevers tells us something about how well they’re working on the whole, even if it doesn’t tell us the precise trend in covid cases.
Another thing that might be possible is to find other sources of data on the actual prevalence of flu, and use that to come up with a better “baseline” which reflects actual current conditions rather than an estimate of the trendline in the counterfactual world where there was no coronavirus pandemic.
A third thing is that 0 is a lower bound on the number of non-covid fevers, so the trend in total fevers is an upper bound on the number of covid cases.
This third thing already tells us something about Seattle (King County). Their peak in excess fevers happened March 9 at 1.76 scale points (observed minus expected), and the March 22 data show the total fevers at 2.77 scale points. As an upper bound, if those are all covid fevers, that is 1.6x as many new daily cases on March 22 compared to March 9. That’s 13 days, and not even a full doubling in the number of daily new fevers. Which suggests that suppression there is either working or coming very close to working (even though the number of confirmed cases has kept curving upward, at least through March 21).
I think that’s right. Although the data still can tell us something after we get into that ambiguous range where it’s hard to distinguish increasing covid and decreasing flu.
One nice thing about this pattern is that it provides some evidence that the anti-covid interventions are reducing the spread of fever-inducing diseases. And the size of the drop in total fevers tells us something about how well they’re working on the whole, even if it doesn’t tell us the precise trend in covid cases.
Another thing that might be possible is to find other sources of data on the actual prevalence of flu, and use that to come up with a better “baseline” which reflects actual current conditions rather than an estimate of the trendline in the counterfactual world where there was no coronavirus pandemic.
A third thing is that 0 is a lower bound on the number of non-covid fevers, so the trend in total fevers is an upper bound on the number of covid cases.
This third thing already tells us something about Seattle (King County). Their peak in excess fevers happened March 9 at 1.76 scale points (observed minus expected), and the March 22 data show the total fevers at 2.77 scale points. As an upper bound, if those are all covid fevers, that is 1.6x as many new daily cases on March 22 compared to March 9. That’s 13 days, and not even a full doubling in the number of daily new fevers. Which suggests that suppression there is either working or coming very close to working (even though the number of confirmed cases has kept curving upward, at least through March 21).