Apparent fatality rates from Covid-19 by age in Orange County, California
Using data for deaths by age and cases by age, we take their ratios to give deaths per detected cases to get the apparent fatality rates by age.
Estimates from the IHME are that in the US and California, only half of cases are being detected by tests. In the US there are almost 30 million cases, and the IHME estimates that there are about 60 million estimated cases. The CDC goes beyond that estimating that there have been 83 million cases. The 60 million would give the estimated fatality rates of a half that of the apparent ones, and the 83 million estimate would reduce to give estimated fatality rates of 29/83 = 35% of the apparent fatality rate.
We give the overall apparent fatality rate as deaths divided by cases, or 4,173/247,641 = 1.69%. This of course depends on what the relative rate of exposures is for each age group, and why we give the table below for apparent fatality rate by age group. A half or a third of this apparent fatality rate may be the estimated fatality rate, or 0.85% for a half, or 0.56% for a third.
Clearly, just looking at fatality rates by age is naive in ignoring all other demographics, as well as medical comorbidities, but that is what we have to start with. It is also probable that comorbidities increase with age. It remains to then separate age as a separate factor from comorbidities
Here are the deaths by age and cases by age in Orange County, California, as reported in the OC Register on March 7, 2021.
As an example, the apparent fatality rate for any age group is equal to:
Percent deaths by age times 4,173 deaths, divided by the Percent cases by age times 247,641 cases.
The ratio 4,173/247,641 = 0.0169.
For the 85+ section, for example, the apparent fatality rate is then:
(32.64/2.14) x 0.0169 = 25.7% fatality rate.
Here is the table of apparent fatality rates for each age group.
| Age Group | Deaths by age | Cases by age | Fatality Rate |
| 85+ | 32.64% | 2.14% | 25.8% |
| 75-84 | 24.35% | 3.18% | 12.9% |
| 65-74 | 19.34% | 6.29% | 5.20% |
| 55-64 | 13.8% | 12.62% | 1.85% |
| 45-54 | 6.45% | 16.06% | 0.679% |
| 35-44 | 2.18% | 15.58% | 0.236% |
| 25-34 | 1.01% | 19.94% | 0.086% |
| 18-24 | 0.22% | 13.81% | 0.027% |
| 0-17 | 0.02% | 10.38% | 0.0033% |
With the overall apparent fatality rate of 1.69%, it is clearly necessary to vaccinate all those over age 55 to get a serious hand on the Covid-19 pandemic.
