Post #582: Need some good news? Rethink yesterday’s blue map.

Posted on March 29, 2020

Sometimes it takes a while for things to sink in.  Yesterday (Post #579) I brought up the Kinsa health weather map.  This tracks trends in rates of fever across the US, as a byproduct of the anonymized data produced by their their internet-connected thermometer.  Like so:

Source:  Source:  Kinsa health weather map.  Blue = declining trend in abnormal amounts of fever, compared to what would be expected at this time.

Now, I’m pretty savvy when it comes to health care data.  So when I saw their map — saw the perfect blue shade of it all across the US — I knew it was too perfect.  I was able to figure out that this probably wasn’t showing anything to do with COVID-19.  In terms of number of cases, common flu is vastly more prevalent than COVID-19.  All this shows is that our social distancing measures have successfully interrupted the transmission of influenza in the US.

All.  (Face-palm).  I said that wrong.  Let me try again.

This shows that our social distancing measures have successfully interrupted the transmission of influenza in the US.

And, you know what?  If those extreme measures interrupted the transmission of flu, odds are good that they interrupted the transmission of  COVID-19.  Which, per the CDC, pretty much spreads by the same mechanism that flu spreads, droplet transmission (with, IMHO, the chance of occasional aerosol transmission.)

Here’s today’s track for overall rates of fever in the US, as of about midnight 3/29/2020:

Source:  Source:  Kinsa health weather map.

As before, the blue band is the prevalence of fever that Kinsa expects to see, based on their projections of the flu season.  I read up on their methodology yesterday, and I’d say they’re pretty good at what they do.  In other words, that blue band isn’t some random guess, it was pretty tight estimate of where you’d expect us to be.

But that prediction is based on normal behavior.  That’s based on normal rates of flu spread, as we go about our usual school, work, and social activities.

Our behavior is now so unusual, we’ve actually driven the prevalence of fever well below the expected level.  To me, the only sensible explanation of that, given the relevant prevalence of disease, is that we’ve accidentally interrupted the spread of flu in the US.  But I’d say that makes it a good bet that we’ve also done what we set out to do, which was to interrupt the spread of COVID-19.

So I can’t yet guarantee you that social distancing is working on the virus it is targeting.  Nobody can.  But, at this point, I can confidently say that social distancing appears to be doing something to some virus.  Probably, due to the vastly larger number of cases, what we’re literally looking at its the impact on flu virus transmission.  But I’d bet good money, based on the similar means of transmission, that this is a crude proxy for interruption of spread of COVID-19.  I’d go so far to say it it strains credibility to think that we could interrupt spread of one and not the other, given the similar means by which they are most commonly transmitted, per the CDC (droplet transmission).

(Other explanations just don’t pan out due to small numbers — e.g., this isn’t the impact of COVID-19 cases being hospitalized and so not using their thermometers, this isn’t the impact of new thermometer sales to the worried-well, and so on.   Case counts are just too small relative to flu, I think. The Kinsa data is a flu-tracking system, and that’s almost certainly what it’s doing now.  The uptick in fevers due to COVID-19 was visible as long as it was seen against a normal background of a much larger number of flu fevers.  But once we interrupted the spread of flu, the loss of those flu fevers swamps everything else.)

COVID-19 has a long “pipeline”, so we aren’t seeing the inflection point in new cases yet.  We’re still observing cases that entered the pipeline two-plus weeks ago (infection) that are now coming out the other end (tested positive).  But this shifts my subjective odds that we’re going to see that inflection point soon.

I should also note in passing that I don’t think this has ever been observed before in the US.  This, being, the interruption of a flu season.  Ever.  That’s how crazily unusual this impact is.  You want crazy crazy?  This makes me wonder whether we might actually see an overall decline in the US mortality rate this year, assuming social distancing is successful.  Not a lot of (e.g.) car accidents happening at present.  In addition to flu deaths.

I have a couple of more things to say, but I’m just going to stop there.  This realization literally brought me awake at 3 AM.  The rest can wait for later today.  On that note, I leave you with a clip from one of my all-time favorite movies, The Emperor’s New Groove.