Post #559: The intermediate and long run for COVID-19

 

Original graph source:  NPR.  Red X is not part of original graph.

If you read these posts, you’ve probably already figured out that this is not a “fun” website.  Or if not, you will shortly.

Edit:  Apparently the Feds came to this conclusion about six days ago, but that has only just today leaked out, per this NY Times article.  Take a peek at the US government response plan referenced in the NY Times article (.pdf).  Assuming that’s not a hoax, if that doesn’t make you say “oh, crap”, you’re not paying attention.


Likely short-run path is known

The short-run path of COVID-19 in the US is pretty clear.  Any number of sources (and Post #550 and Post #555 and Post #557) tell you that:

  • known US cases will continue to grow rapidly (#550),
  • that will likely continue to the end of March or so (if our “social distancing” such as school closings works (#557),
  • at which point growth in new cases will decline (the “inflection point), but
  • probably, death counts will continue to grow beyond that inflection point, because it often takes a while to die from this (Post #551).

If the US version of social distancing works (still an unknown at this point, and will not be clear for another week or two), then the short run prediction isn’t much more than a few bits of simple arithmetic.  


But what happens after that?

Now I’d like to have a better idea of what happens after that with COVID-19.  This assumes we can contain the pandemic and so avert mass deaths in the short run. Assuming that we “flatten the curve”, what happens next.

And, ultimately, “what happens next” seems like just a bit of common sense and simple arithmetic.  If you haven’t gotten COVID 19 yet — and that covers 99.998% of the US population — you remain at risk for it.  So doesn’t that mean that if we let down our guard, the epidemic just picks right back up again? 

The short answer to that appears to be yes.  Yes, at least until an effective vaccine is produced and distributed.  Yes, even if we succeed in containing it, if we relax the current restrictions, the epidemic restarts. That’s the best available estimate, as of now.

The formal modelling of this is presented in a paper released Monday by a team of researchers at the Imperial College of London (.pdf).  There, when talking about the “social distancing” measures currently in place (e.g., closing schools and so on), they conclude (emphasis mine):

" ... this type of intensive intervention package – or something equivalently effective at reducing transmission – will need to be maintained until a vaccine becomes available (potentially 18 months or more) – given that we predict that transmission will quickly rebound if interventions are relaxed. We show that intermittent social distancing – triggered by trends in disease surveillance – may allow interventions to be relaxed temporarily in relative short time windows, but measures will need to be reintroduced if or when case numbers rebound."

The upshot is that the “flatten the curve” graph that you have probably seen is misleading.  Hence the red “X” on the graphic above, where the cases fall to zero.  That ending appears unlikely and/or the timescale is completely wrong.  A more accurate depiction is probably something like this:

Original graph source:  NPR.  Original Source (obscured on drawing):  CDC, Drew Harris.  Original Credit (obscured on drawing):  Connie Hanzhang, Jin/NPR.  Wavy blue section is not part of original graph.

And that blue section continues until such time as an effective vaccine is developed, produced, and distributed.

In fairness, I guess I should bring up the possibility that COVID-19 might disappear on its own.  But as I read it now, that’s not what the professionals in this area think will happen, for several reasons.

My reading is that that would be an unlikely outcome.  The reason is that COVID-19 lacks the characteristics that would make eradication possible.  For example, both SARS and MERS are novel deadly coronaviruses that emerged this century.  SARS was eradicated (per the CDC), while MERS is still active (per the CDC) but doesn’t pose a pandemic threat.  The key differences are that those coronaviruses are vastly harder to transmit from person-to-person, and individuals don’t spread disease until they reach the point at which they have symptoms (reference).  That’s the opposite of COVID-19:  easily spreads person-to-person, and can be spread before symptoms emerge.

The upshot of this is that nothing is free.  Assuming that social distancing measures such as school closure work in the US, all we have done for now is convert COVID-19 from an acute crisis into a costly chronic condition.  We we will need to maintain (all of, part of, or maybe even more of) the social distancing measures currently in place if we want to continue to avoid that acute crisis.  Until such time as we can get the US population vaccinated against it.

The only thing I would question at this point is the widely-cited figure of 18 months to develop a vaccine.  What does that mean?  Does that mean it typically takes 18 months to develop a vaccine in normal circumstances?  Or does that mean that even a Manhattan Project level-of-effort and expense could not speed that up materially?

Because, for sure, every day we have to live with the current set of “social distancing” restrictions is costing us hugely.  Not just the money cost of lost business, and the lives lost, but the loss of a year of education for US children.  Any expense for vaccine development has to be a drop in the bucket compared to those costs.


Addendum

I may or may not work out a few more details of this in some subsequent posts.  Mostly, I’m writing these to make sure that I understand what’s going on.  My wife tells me that my explanations tend to be clear, and so its useful to publish them.  If they are helpful to others, that’s great.

I’d like to get a grip on just how unlikely eradication is.  In particular, I think I know why flu disappears in the warmer weather:  high humidity destroys the virus as airborne particles (reference 1), and low humidity compromises some immune responses ( reference 2).  There’s some hint of something like that for COVID-19, but nobody is counting on it just disappearing over the summer (Washington Post).  I’d also like to know whether or not vaccines have ever been produced in under 18 months.  Because, barring one of those two events, we’re kind of stuck in this social distancing limbo for the next year and a half.  Or we give up, have the acute pandemic, and get it over with.  No good options either way.

I guess the final thing I have to say is that, after SARS and COVID-19, how many times does this have to happen before the Chinese figure out that routinely slaughtering exotic wild animals for human consumption is a fairly stupid thing to allow in the 21st century?  Based on what I can read, I blame the entire world-wide pandemic on that foolish practice.  Let’s not lose sight of that as this unfolds, or we may be repeating this another decade down the road.

The Chinese have been pushing the idea that their authoritarian model of government is superior to traditional western liberal ideology.  I’d say it’s time for the Chinese to put up or shut up.  Why can’t they shut down their exotic animal trade?  I mean, it’s great that they got a grip on their epidemic in record time.  Now the rest of us have to deal with what they started.