Forecasting the Reopen

A new antibody study, based on a more-or-less random sample, indicates that around 3% of Santa Clara CA County residents are immune to covid. That’s about 50 times the number who have tested positive for the virus.

In my first post in this series I estimated that the actual prevalence of the disease in the US population was about about 30 times the number of test-confirmed case — not far from the Santa Clara estimate. Let’s split the difference. The current confirmed US case count stands at 710K: increase that number fortyfold and you get 28 million, or over 8 percent of the population. For the past couple of weeks the daily count of newly confirmed cases has plateaued at about 30K per day, which means that the actual rate of increase might be 30K x 40 = 1.2 million daily. At that rate 60% of the total US population of 320M will have been infected by the end of the year, bestowing herd immunity on the nation and extinguishing the epidemic. That’s assuming that current social distancing measures remain in place — which they certainly will not.

But, if the Santa Clara estimates of contagion rate are anywhere near accurate, and if the daily deaths aren’t dramatically undercounted, then the mortality rate would be 2.2K/1.2M, or 0.18%. That’s still twice as high as the flu, but not nearly as high as original estimates of around 2%. Herd immunity would be achieved at a cost of around 350,000 lives.

Let’s assume that a relaxation of social distancing will double the contagion rate. Herd immunity could be achieved by September. Let’s further assume that, motivated by self-preservation, those most vulnerable to the disease — the old and the comorbid — will continue to self-quarantine. That sector accounts for around 85% of the covid deaths. So while the infection and death rate of the young and healthy will double over the next few months, the most vulnerable demographic will continue to fall ill and die at around the present plateaued rate. The same death rate extended over only half the duration means that only half as many of the most highly vulnerable people would die from the disease before the epidemic runs its course. Total deaths would be cut from 350K down to 220K. With more informed treatment protocols and more fully equipped hospital facilities, maybe the number can be cut to 200K. That’s pretty darned close to the body count estimate generated by the CDC-Homeland Security Joint Task Force, explored in a post from a few days ago.

Flattening the curve — that was the original rationale for social distancing: to slow the rate of contagion so that the medical system could keep up. For the past two weeks the US curve has been flattened. If the plateau persists, then the virus will continue to spread through the population at a steady rate, with newly infected people replacing those who have achieved immunity or died.

Reversing the curve — that hasn’t happened, at least not yet. The IHME model projects a dramatic decrease in new cases and in deaths, nearly zeroing out by mid-May. That’s only a month from now. We’re only 3 days  past what the presumed peak day, so it’s still too early to say how closely the actual situation will conform to the epidemiologal model. But the IHME also forecast that the counts would already have come down from their peaks in Italy, Spain, and France, and that hasn’t happened yet either. Maybe the post-peak drop will never materialize; maybe flattening is all that can be expected from widespread social distancing.

Getting ahead of the next curve — that’s what Trump’s guidelines are all about. But the infrastructure for testing and isolating and contact tracing isn’t in place, the individual states are strapped for cash and expertise, and the Feds aren’t stepping up with the money or the technology or the personnel to make it happen. It took less than 24 hours for Trump to pull the rug out from under his own guidelines. LIBERATE MINNESOTA!  he tweeted. LIBERATE MICHIGAN! LIBERATE VIRGINIA and save your great 2nd Amendment. It is under siege!  Does Trump have evidence that these three states meet the first set of criteria for beginning the first phase of gradual reopening? None of the three comes close to passing the only criterion for which publicly available data can be ascertained — “Downward trajectory of documented cases within a 14-day period.” Public protest against lockdown in states with Democratic governors would seem to satisfy Trump’s personal liberation checklist.

So let’s assume that the country is going to reopen, piecemeal but in short order, absent downward trajectory and irrespective of preparedness. Will all hell break loose, with coworkers and students, beachgoers and barflies getting up in each others’ faces? Or will people act with at least some sense of self-preservation and decorum, knowing that the virus is still on the loose and looking for new hosts to colonize? Will school administrators and students/parents recognize that it’s in their mutual best interest to screen attendees every day for fever, sending the sick ones home until they recover? Will employers and employees? I’m guessing we’ll end up somewhere between utter disregard for contagion and total lockdown. And I’m guessing further that the aged and comorbid, strongly motivated to stay home, will continue to do so at current levels.

If things open up again, and if the Santa Clara immunity results prove to be accurate and generalizable, herd immunity will likely be achieved by November 2020, with a body count of around 210K. Dreadful, but maybe unavoidable. A few other countries have been able to quell the initial wave and to prevent subsequent waves from forming, keeping the death counts low until a vaccine is developed. The US has the technological savvy, the money, and the managerial and logistical capabilities to do it too. But it’s like a lot of other frustrating developments in this country — no reason it can’t happen, no way it ever will happen.

 

 

 

 

5 thoughts on “Forecasting the Reopen

  1. The clever Swedes (are they?) probably are doing tests on the quiet to find out how herd immunity is getting along and cynically amongst the large immigrant community who are less compliant probably than the ethnic Swedes who will abide by recommendations. They are getting the numbers or the one that counts: the deadly denominator.

    Liked by 1 person

    1. Probably so — Sweden’s public health service seems to be calling the shots, and they’re more attuned to data collection than are the politicos. Sweden slipped into moderate social distancing without getting over the hump on the initial wave — a pathway that the US will likely follow soon. Publicly available data on Swedish new case counts and deaths seem to swing wildly from day to day, making it tough to discern whether upward trends are accelerating or have plateaued at a steady rate of increase.

      In the US too it’s racial minorities who are feeling the brunt, for a variety of reasons: densely packed neighborhoods and multi-generational households, jobs in “essential services” that can’t be performed at home, higher proportion of comorbid conditions, less access to free/inexpensive healthcare. A recent study conducted in Philadelphia indicated that African-Americans were slightly *less* likely to adhere to social distancing guidelines but slightly *more* likely to stay at home, so those two findings would tend to cancel each other out.

      Liked by 1 person

  2. “We’ll take thousands of tests, antibody tests, over this next week all across the state to give us a real snapshot, a real baseline, of exactly how many people were infected by coronavirus and have the antibodies,” Cuomo said. “So we’ll have the first real statistical number on exactly where we are as a population.”

    New York has 250K test-confirmed cases; if their statewide survey comes close to replicating the Santa Clara numbers, then half the state will turn out to be immune. Wouldn’t that be something.

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    1. When last I checked, a week or two ago, the mutation rate had been minimal since the pandemic began — much lower than the flu virus. So that bodes well for at least medium-term immunity of those who’ve recovered, as well as for potential effectiveness of the vaccine if and when it gets rolled out.

      Liked by 1 person

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