We’ve discussed numerous times this question of, how deadly is COVID19? Or to put it more technically, what is the infection fatality rate (IFR) for the disease? What percentage of people who get infected die from it?
There are a host of technical factors and data we don’t yet have that go into answering this question. But I want to share with you something I just happened upon. If you look at the current New York State serology study and use an apples to apples comparison of the COVID19 death toll in New York City and New York state, it generates an IFR that is basically identical. For the state it’s .88% and for the city it’s .87%.
Now, I don’t suggest that this is a definitive number. This is something that will take years and lots of research and analysis to ascertain. But here for the first time we have data, albeit preliminary and wobbly, for the variables that make up the calculation.
Here’s my work.
The state serology study (as of May 2nd) has tested approximately 15,000 people across the state and found that 12.3% state residents have antibodies and 19.9% in New York City. If we apply those percentages to the 2019 Census estimates of the respective populations we get 2.428M infections in the state as a whole and 1.671M for the city.
COVID19 antibodies tests are new and many are not terribly reliable. But New York state appears to be using one that is much more reliable – one that the state created. New York’s high prevalence of COVID19 also makes it more possible to deal statistically with false positives. As we’ve discussed elsewhere, in states where the prevalence is similar to the rate of false positives your results basically don’t tell you anything.
Now here is a critical point. New York City is one of the few jurisdictions releasing mortality data for confirmed cases and “probable” ones. This means deaths with a lab confirmed COVID19-positive test and those diagnosed on the basis of symptoms but no test. The combined number is almost certainly closer to the accurate death toll. But New York State, like virtually every other place in the country, is only releasing the lab confirmed number. To do this right we need an apples to apples comparison. So here I will use the lab-confirmed numbers for both jurisdictions.
This gives us …
21,478 / 2,428,000 = .88%
14,482 / 1,671,000 = .87%
If we used New York City’s combined number of confirmed and probable deaths, the rate would be 1.18%. That is likely closer to the ‘true’ number. But again, the point here was to see if the serology data and mortality data pointed to a similar rate in both jurisdictions.