Thursday, April 30, 2020

Projecting Deaths from COVID-19 (another update)


On April 2, I published a blog (here) analyzing available information to put into context the 100,000–240,000 U.S. COVID-19 deaths then being projected. On April 15, in this blog, I cast doubt on the reduction of government projections to “only” 60,000 deaths through August 4[i], suggesting that 100,000 deaths were more likely. The official projection has now been increased several times and as of this writing sits at nearly 73,000. Once again, applying my na├»ve methodology, I think this number is too low.

A chart I have found helpful to visualize the path of U.S. COVID-19 cases is to compare us to Spain, Italy, and Germany, recognizing that Italy started about two weeks before us and Germany and Spain a week after that.

Note: the horizontal axis is time (Italy has 64 days, the other countries fewer.

The most recent two weeks have crushed any chance the U.S. curve would flatten faster than Italy’s. Instead, our path is not even flattening as much as Italy’s did at comparable points in time. We have set our own course and it appears it will remain above Italy’s level of infection.

Fortunately, the death rate experienced in the U.S. is considerably lower than Italy’s. Using the metric developed in earlier posts of dividing total reported deaths by total reported cases a week earlier (in order to reflect an average time between reporting and death, should it occur), the U.S. is now at 7.3%, less than half Italy’s rate. The chart below demonstrates that both rates have been declining very slowly for some time.


Before combining the data from these charts to project future deaths, we need to examine some assumptions.

Why Are U.S. cases as a percentage of population increasing faster than Italy?

Either (1) U.S. testing is more comprehensive than was the case in Italy, resulting in more “benign” cases per capita detected in the U.S. than in Italy. AND/OR

(2) Italy did a better job of controlling the spread of the virus through the strength of and/or compliance with stay-at-home orders, business closures, and similar precautions.

If U.S. testing had significantly increased, yielding many “benign” cases, we would expect mortality rates of those infected to decrease. Over the last two weeks there has been a slight decline in the U.S. from 7.5% to 7.3%. If the explanation for the decreased death rate were entirely due to increased testing, it would mean that about 22,000 of the 412,000 cases reported between one and three weeks ago resulted from increased testing. Adjusting U.S. reported cases by that amount only slightly decreases the slope of the U.S. curve displayed in the first graph.

If next week we see a significant decline in the death rate, we’ll know increased testing is driving the level of newly reported cases. That would be a good thing.

In the U.S., states have imposed various levels of business closings and stay-at-home orders, making it difficult to compare to Italy, which did have different rules for the northern and southern sections of that country. I don’t have data to know how well Italians complied with their government’s rules. Anecdotal evidence in the U.S. shows compliance has been spotty. Some churches remained open despite state rules against crowds larger than ten people Demonstrations occurred in several state capitals protesting the “unnecessary” sheltering in place. Beaches in some states remain busy, where other states have kept them closed.

My current projections

As I write this (the morning of April 30), the U.S. has reported 1,064,194 COVID-19 cases of whom 61,656 have died. If we had no additional cases and the death rate remained at its current level, we’d have 77,000 deaths (4,000 higher than the government’s projections that go out to a later date).

If we continue to track Italy’s path (but recognizing our current level is higher than theirs) we would experience another 290,000 cases, which would yield another 21,000 deaths for a total of 98,000 by May 15. However, I do suspect death rates will continue to decline as they have in Italy. Should they decrease in the U.S. to 7%, the expected deaths by May 15 becomes fewer than 95,000—still much higher than the government’s estimate of 73,000 by August 4.

Italy continues to report new cases, and so will the U.S. We don’t know the effect warmer weather will have on stopping or slowing the spread. It happens for flu, so we can hope. Offsetting that are whatever negative effects may result from states “reopening” their economies by relaxing the disease-preventing rules currently in place.

I’m starting to think 100,000 deaths might prove optimistic, but I continue to hope I’m wrong.


No comments:

Post a Comment