Tracking Covid-19: Update

This article is an update to “Tracking Covid-19” that Al Pfadt, Kathryn Whyte, and I wrote last week. In that article we summarized what is known about Covid-19, what has already happened, and what is to be expected based on the analysis of the data and the epidemiological models.

Over the past week the curve of Covid-19 infections in the United States has slightly flattened. Here are updated graphs of the actual data and new projections for what we can expect in the next few weeks.

Figure 1 shows the number of confirmed cases of Covid-19 in the United States as of 7 a.m. each day. These are the values posted by the European CDC at noon London time, and so they are slightly smaller than some other values that are reported later each day.

Figure 1: Number of confirmed Covid-19 cases in the United States

While the number of confirmed cases doubled every two to three days during the first four weeks of March, the counts are no longer growing at that rate. The curve in figure 2 has flattened somewhat. Fitting a line to the last few points by eye and extending it forward we can see that the United States is on track to hit one million confirmed cases sometime around April 21.

Figure 2:  Confirmed Covid-19 cases in the United States

It is important to note that, unlike so many others, this projection is not based on some complex mathematical model. Mathematical models always require assumptions, which will generally reflect the author’s point of view. Rather, these projections are simply the actual current data extended into the future. If we are able to further flatten the curve we should find the future values falling below the projections. If the future values fall above the projections then our efforts to mitigate the infection are faltering. These graphs are  nothing more or less than our report cards.

Figure 3 below contains the data for the number of Covid-19 deaths in the United States.

Figure 3: Number of Covid-19 deaths in United States

While there has been a slight flattening of this curve over the past week, the deaths are still  increasing by 11.6 percent each day. This gives a doubling time of about every 5 days (compare 4/12 and 4/7). At this rate we have the potential of reaching a total of 100,000 deaths by April 25, as may be seen from the straight line projection in figure 4.

However, deaths lag behind the confirmed cases, and the confirmed cases curve has flattened. They are increasing about 7 percent each day which gives a doubling time of about 10 days. So, a more conservative projection for the number of deaths can be had by using the curved projection arrow where the deaths taper off to a daily increase of 7 percent. Here we project a total of 50,000 deaths by April 25. Hopefully the number of deaths will fall short of this projection.

Figure 4:  Covid-19 fatalities in the United States

For more information about these graphs and Covid-19, see “Tracking Covid-19” in the April 6 edition of Quality Digest. Readers are encouraged to print out this update and plot the daily numbers on each graph for themselves. Hopefully they will fall below the projections.

You can also download this Excel spreadsheet, enter the daily numbers yourself, and have a similar graph automatically updated for you.

Also, this simple Excel spread sheet should help show the difference between a linear vs. semi-log chart for showing exponential data.

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