Mortality Discussion from April 28, 2020

Now, a thought or two about mortality. On April 23rd NY reported completing a somewhat random test of 3,000 New Yorkers for COVID antibodies. https://www.newsweek.com/test-shows-21-percent-new-york-city-residents-who-gave-samples-have-coronavirus-antibodies-1499878

Tests were done earlier that week for randomly selected individuals in grocery stores and shopping centers. Of the 3,000 tested, 15.9% were shown to have had the COVID infection. Since that time, New York has revised that number up to 16.9%. This is incredibly useful information, and provides us with a first meaningful clue about mortality. I first did a rough calculation of NY mortality rate by extrapolating the random test results to the NY population, then aligned deaths with the exposure period. From this I calculate a mortality rate of 0.53%. This is not unexpected, but it is much more interesting when broken down by age. When I look at cohorts of age 60 and over, and 59 and younger, and go through the same calculations, I get an estimate of mortality rate for these two age groups of:

Age Mortality Rate
0-59 0.09%
60+ 2.50%

Now there are lots of issues with my calculations. First, although the sample may have been random, there was some self-selection, as the sample pool was composed of those willing to leave their homes, which I bet skewed younger and less risk-averse. I also do not have a demographic breakdown of the sample. The only thing I know is that no one over age 75 was sampled. This is a major issue, as over ½ of all deaths in NY are over age 75. This leads me to believe that COVID prevalence is actually lower among the 60+ cohort, and higher among the 59- cohort. As a result, I believe that the mortality rate for the elderly is higher than that calculated above, and the mortality rate for those under 60 is lower than that calculated above. By the way, I would have preferred to use an age 65 cutoff, but unfortunately the NY Department of Health only reports deaths in deciles. Ideally, if I had the data, I could study mortality in 2 cohorts – those over 65 or with certain co-morbidities, and a second group of under 65 without certain co-morbidities. I believe you’d find a mortality rate in the first group well over the 2.50%, and the mortality rate in the second group much closer to nil.

So as we recover as a society, the methodology seems to settled that we’ll unlock one geographic area at a time. But we have 2 easily identifiable populations, once with relatively high risk, and one with a tiny fraction of the risk. It occurs to me that we could more safely unlock by doing it demographically, rather than geographically. We could extend shelter in place rules for seniors and those with definable risk factors, and eliminate them for the under 65 and healthy population. It would also be fairly easy to define perhaps one concentric circle around the vulnerable by maintaining shelter in place rules for certain caregivers and health care workers. So that’s my message for today: Unlock Demographically, Not Geographically.

I’ve already received quite a few questions about the mortality rates I quoted this morning, which were:

Age Mortality Rate
0-59 0.09%
60+ 2.50%

The common question is “what does it mean?”. These mortality rates represent the probability of death for those unlucky enough to be infected. The general population mortality rate (the probability of someone generally dying from COVID) is much, much lower. So these rates can be interpreted as “a person contracting COVID and age 59 and under has a 0.0009 chance of dying from the disease. Put another way, for every 1,111 people under age 60 contracting COVID, 1 would be expected to die. For those over 60, the number is about 1 out of 40, a remarkable difference.

The second question I received in numbers was “is 0.09% low or high – relate it to something”. OK, so in the general population in the U.S., the average 50 year old has a 0.5% change of dying within a year (sorry for that news). This probability is roughly 5 ½ times higher than the probability of dying IF YOU CATCH COVID.

For the average 75 year old in the U.S., the probability of dying within one year is 3.6%. This is about 1 ½ times higher than the probability of dying IF YOU CATCH COVID.

How can this all make sense? Well, it seems Actuaries dwell on this the most, but each year about 3,000,000 people die of all causes in the U.S. When all is said and done, it looks like COVID deaths in the U.S. this season will make up about 2-3% of that number.

I’m going to pin this and this mornings mortality discussion to the bottom of the reports, since many new people join this list every day.