10. Weekly Update: The World is Recovering

(4/15/20) Nearly all hot-spot countries and U.S. states are near or past the peak for death rate. That means the number of active cases (prevalence) is on the decline and some amount of social easing can be reasonably considered. However, until our population is largely immunized by having had the disease or by vaccination, social interactions cannot return to normal.

Remember to check my post called “Daily Rumblings” for late breaking updates.

Our model has been described in previous posts so we can spare that detail for now! Let’s put it to further practice and use it to help inform us on when we can start to relax social distancing and to what extent. We begin by showing the latest death rate plots for hot-spot countries and U.S. states below. Now that these curves have developed toward and past their peaks we superimpose a Gaussian function to visualize the progress made by these populations.  Note that we have de-rated the severity of several of these populations as represented by the colored circles. Major recovery is evident, and as predicted, about 3 weeks after serious social distancing was implemented.

The qualitative red, yellow, and green rankings reflect accelerated, rolling over to a peak, and well on the decrease death rates, respectively.

We make the following comments:

  • The Gaussian dependence in most cases represents well the reported death rate data (even while fixing the width at half max to 4 weeks). This dependence, and the symmetry assumed by the Gaussian, is expected to get distorted due to interventions to reduce the rate, e.g., social distancing. The breakdown in the fit is evident for those populations who were most aggressive, such as China and S. Korea, the latter never reaching exponential growth and the death rate instead being more constant.
  • Once a country reaches the peak in death rate, it is about half way to its final death count.
  • Italy and Spain are making remarkable progress and we (perhaps prematurely) have upgraded their situation to green (out of trouble). How they manage their retreat from social isolation will determine how successful they will be in the long term. This is the topic for below.
  • The U.S. is lagging these other countries in reaching a peak; however, it does appear that the peak is imminent.
  • Regarding the U.S. states: Washington is past its death rate peak and has been upgraded to a green. California never saw high death counts, just high death rate that appears to be peaking so we upgrade that to yellow (warning).
  • We have not followed MI, NJ, and LA from the beginning so we have limited data to fit to the Gaussian, but each of these states is making progress and if the current trends continue over the next week, they will all be upgraded as well.

We now present our familiar table for forecasted total deaths, prevalence (current cases), and incidence (new cases) along with their values per capita (per million people). We also add a new column for the date we consider to be the earliest each population base can begin relaxing social distancing. We will tentatively call this an easing date and not a safe date so as not to conjure up excessive hopefulness.

Assumptions: Mortality factor is estimated as 1.0% for most favorable populations (not yet strained health care system) and up to 2.0% for least favorable populations (strained healthcare system).

A rough rule of thumb is that the easing date cannot be before the point when the prevalence count drops to less than what it was when the death rate took off. If that was about 4-6 weeks before the death rate peak, then one might think it should be about 4-6 weeks after the peak since the rise and the fall is approximately symmetric. However, as I showed in the previous Post #9, the incidence and prevalence curves precede the death rate curve by about 2.5 and 1.25 weeks, respectively, and that results in the prevalence count coming down to its say minus 5-week mark at about 4 weeks after the death rate peak (this time accounts for decreasing incidence and recovery from the disease). Now this date would not be safe because it corresponds to a prevalence that previously set off the exponential growth in death. However, if we exercise some precautions then sometime soon after 4 weeks may be considered safe.

For our purposes, we assume that as an absolute minimum condition to consider some social relaxation, that the prevalence must drop below 100 active cases per million (i.e., 1/10,000 people). One would still have to ensure that close contact with strangers is minimized and voluminous testing must be continued among other moderation. Frankly, we can never return to normal until some high percentage of a population is immunized either by having had the disease or by vaccine. A ballpark figure is about 50%, but no population yet has had more than 10% infected (Projected by 6/1/20: Italy ~ 4%, Spain ~ 5%, U.S. ~ 2%, NY ~ 10%).

Main comments are:

  • Without making a pretense about safety, our forecasts for when it is reasonable to consider social relaxation are given in the right most column in the above Table.
  • China and S. Korea are already relaxing social isolation so the rest of the world has many weeks to observe the prudence of their approach and decide on some combination of emulating and modifying.
  • Iran would appear to be the next country to drop below the 100 per million prevalence threshold (4/29/20). Italy and Spain follow next in the beginning of May and the U.S. and U.K. not until mid May.
  • Regarding the U.S. states it is not prudent to consider social relaxation for any of the hot-spot states before mid May except for CA and WA for which early May may suffice. NY will not reach an easing date until about 5/19/20.

Finally, we provide an update on the comparison of our forecast of critical values to that of the Institute for Health Metrics and Evaluation (IHME) at the University of Washington (UW), which has emerged as perhaps the leading model for informing our nation on the state of COVID-19 (http://www.healthdata.org/covid/).

We appear to be tracking very closely indicating that there must be components of each model that are similar. We tend to forecast a little earlier from peak rates. As the death rate curve flattens the accuracy of forecasts improve greatly because it is more evident where in the rise and fall cycle a given population is. This also accounts for the better agreement between the two models relative to previous weeks.

2 thoughts on “10. Weekly Update: The World is Recovering”

  1. First, very sorry for your personal loss in all this mess! Condolences.

    I think you may be missing a bigger picture here. There seems to be a belief that social distancing will prevent further outbreaks in other areas. This is not what the evidence suggests. I see the virus radiating from New York like a giant wave and it is just now reaching neighboring northeast states. They are all accelerating rapidly still. So is Florida. Maybe there is a presumption it won’t explode as much in these areas because tests are moderating and social distancing but these assumptions have flaws. (1) We know testing is highly limited so how do you trust those numbers? See Jack’s Blog #1 (2) Are people REALLY social distancing enough? We will find out! I suspect not, however.

    Further, in terms of re-opening, we still have a mess. Many areas have not had outbreaks. Testing is limited. Antibody tests don’t exist. Now there are reports you can be re-infected (I have doubts but see my next point…). I also possess credible information there are 8 strains of COVID-19 circulating now, which could turn into a vaccine nightmare. We’re also seeing new surges in South Korea and China this week. I personally don’t know the way out of this but I know my opinion isn’t being solicited anyway so I’m not going to try to solve it.

    Finally, I will dispute your conclusion again. We will hit 60,000 by mother’s day. While the deaths aren’t accelerating, I see clear evidence we will maintain 2000 deaths per day for up to a month because other regions will accelerate as NY/NJ falls. I think Bill Gates is probably right that the target to really open up is really Father’s Day if we don’t want further outbreaks.

    1. (1) I already addressed your first paragraph in my reply to your comment to Post#9. Basically new outbreaks are reflected in the U.S. data, so overall the U.S. doesn’t recover as fast as individual states that were first to see rampant growth. Yes there will be new outbreaks but they are occurring in less populated areas. We first talked about NY, NJ, then MI, IL, LA, and now states like SD, etc. But I agree these new hot-spots are difficult to predict, other than they will happen. MA and CT are really taking off, which is concerning.
      (2) In terms of re-opening, that is regional dependent as clear from my table. WA as early as 5/5/20 but NY not until at least 5/19. Any new hot-spots will have to wait their turn to recovery. And by easing date I mean by no means loosen anything before that date and after only with measured restrictions in place.
      (3) Re-infections are believed to be due largely to infections of patients who had false positive diagnoses (they never actually had COVID-19). The tests have about 95% specificity and 95% sensitivity, which is actually pretty good for screening tests in general. But the sensitivity figure means that about 5% of those with COVID-19 who are tested come up with a negative result. The specificity means that 5% of those taking the test will come up falsely positive. Now imagine that in a group of people of say 100 there are 5 true COVID-19 carriers. Then the test will detect these 5, but will come up with 5 other false positives. So it is possible that half of the confirmed COVID-19 test results could be false positives. Scary to think about but a good reason to only test suspected patients, at least during the peak of infections.
      (4) I don’t see any new surges in China and S. Korea from the official data: New deaths per day for the last week are: China: 2,2,1,3,0,2,0 and S. Korea: 8,4,4,0,6,3,5.
      (5) No disagreement on Mother’s Day. My number of U.S. deaths by then is about 55,000.

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