Thursday, April 09, 2020

The Case for Staying Home - The End of the Beginning

Winston Churchill, 1942

Now this is not the end.

It is not even the beginning of the end.

But it is, perhaps, the end of the beginning.

There are a couple of very important milestones to consider when we think of getting through this Covid-19 crisis.

1) The day that the number of new daily cases peaks, and each day after that we have fewer new cases than the day before.
2) The day that the number of new cases reaches zero.
3) The day that the number of existing cases reaches zero.
4) The day that we are confident that the number of asymptomatic carriers reaches zero.

For Los Angeles, Italy, Australia, and a bunch of other places, we have passed the first milestone.  We are truly at the end of the beginning.  Now, we need to see how quickly we reach the beginning of the end.

The reason that I'm mentioning this, by the way, is that I've seen a number of different reports that talk about a given location "peaking".  Yet, without context, we don't know what peak is being referred to.  The Institute for Health Metrics and Evaluation (IHME) has a brilliant set of analysis, where they talk about "peak hospital resources use" and "peak deaths".  These are both incredibly important metrics, but not what I'm discussing.

Last time I put up a graph which showed the peak of new cases for Italy.  I showed that Italy peaked on March 24, exactly 14 days after their March 10 stay at home order.  However, at the time, we didn't know how Italy's decline would look.  Now we do (apologies for the formatting - I wanted this to be legible):

We can see here that Italy is dropping at a steady rate of roughly 120 fewer new cases each day than the day before.  This doesn't mean that Italy is curing people at the rate of 120 people a day.  It means that, on April 9, Italy had 4204 new cases in the prior 24 hours.  Therefore, on April 10 (tomorrow), they will have only 4084 new cases in the previous 24 hours.  Because of the bounciness of the curve, this exact number is unlikely, but the trend is reasonably good.  If this continues linearly (and I really don't know if that's likely, or if it is set to accelerate or decelerate) then we can predict the day that Italy hits zero new cases.  Currently, that day is May 14 (Edit: with the original figure, this was April 30).  We can also predict the final number of infected, which would be 215,166 (Italy currently has 143,626 (again, all data from Johns Hopkins).  So, even though Italy is past their peak, over 60,000 more people are expected to contract the virus  before they finally get through this first wave (I'll talk more about subsequent waves later).

Given that I live in Los Angeles, I've been tracking LA with specific interest.  I had been hoping to see that we would demonstrate the same peak as Italy.  It took a few days to verify it, but since LA shut down on March 19, we should have seen our peak on April 2.  It looks like we could say it actually happened on April 3.  And, like Italy, there is now enough data to make an early prediction on the rate of decline (and, like Italy, I'm speculating that this decline is linear and I don't know if it will be).  Based on the last week, it looks like LA's new cases are declining at a rate of 21 fewer new cases/day (interesting fact, if we were to decline at the same rate as all of Italy, adjusted for population, that would be 20 fewer new cases/day - so we are seeing an extremely similar type of response).  Based on this projection, Los Angeles county will see zero new cases on April 29 with a total infected count of 12,045.  As of April 9 we are at 7955, so, like Italy, we still have about 1/3 of the way to go, and over 4000 people will become confirmed cases before the end of April.

However, this is all good news.  I think we can safely say that we are past milestone #1.  Now, the US as a whole is in much worse shape and I will continue to track the many states that are just beginning their infection ramp.

So, if this the end of the beginning, what is the beginning of the end?  There are two.  The first is a period after the zeroth new case.  If we assume that it takes 14 days to present possible symptoms, then we would want to see at least 14 days of zero new cases (ideally, much longer).  We want to make sure that all lingering infections have run their course before we lift social distancing measures.  Mayor Garcetti here in LA talked about us staying indoors until the end of May, and based on these numbers, that seems like the right plan.

The second "beginning of the end" is actually the next 12-18 months.  Until a vaccine is discovered and widely deployed, or herd immunity is reached, there will inevitably be flareups.  And, then, unless we act differently, we'll be scurrying back into our houses for another 3 months all over again.  Additionally, because, at least in the US, we have such a large population of states that are treating this virus with widely different levels of seriousness (from "adult and listen to the science" to "childish and criminal" a la Mayor Vaughn of Amity in the movie Jaws) we will have a secondary explosion just from people traveling within the country from one state to another.

So, the solution is twofold.  First, we must do like Germany, and implement widespread national testing for antibodies (I had a link here to FT, but it seems to only work if you go via Google).  This will allow us to know who is immune, and how widespread our herd immunity already is.  This allows us to get the economy restarted.  Second, we must do it right this time (like South Korea) and implement testing and case tracking and isolation to quickly pounce on flareups to allow us to stop the fire before we end up with another inferno.  This period will likely see social norms of continued mask-wearing and fist-bumps, rather than handshakes, well into 2021.  Remember that the Spanish flu of 2018/2019 had three severe waves.

So, we are not at the beginning of the end.  We likely are only 1/3 of the way through our quarantine and we must not relax our efforts to isolate (and we must have the utmost sympathy for the horrors to be witnessed by states that are have only recently entered their quarantine).  But, like Churchill said, we are likely at the end of the beginning.  And there is real comfort in that.

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