Many people are asking why COVID-19 death counts in the USA are decreasing or stabilizing if the number of confirmed COVID-19 cases are soaring in most of the USA. The governors of many of the worst-hit states such as Florida, Texas, Arizona, and California are attributing much of the rise in cases to increased testing of milder and asymptomatic cases which tend to not require hospitalization nor result in deaths. In fact, many of these states did experience dips in Case Fatality Rate (CFR = deaths/cases) as the denominator increased faster than the numerator. While this was true in May, it is no longer true in June. The reason is that in many states such as Florida the number of tests performed daily (brown squares against the left axis in the figure below) increased impressively in April and May but has stalled in June to the extent that the percentage of tests returning positive (blue diamonds against right axis) has increased to new highs.
The governors also argue that newer cases tend to skew younger as they are the least likely to wear masks and observe social distancing. This can be seen in the next graph that shows the distribution of new cases in Florida by age group from 6/19 to 6/23. While the age distribution cumulative to 6/19 (blue bars) had a median age of 45 yrs, the incremental 15,073 new cases (brown bars) over 4 days had a median age of 35 yrs.
The younger patients tend to require less hospitalization and die less often. The following graph shows the very strong CFR dependence on age. The same age dependence seen in Florida is also seen in California and throughout the world. Those younger than 30 yrs do get sick but <0.1% will die from COVID-19. Those older than 50 yrs will have >1.0% chance of dying from COVID-19. Nearly 1,000 new cases for those older than 50 yrs have been confirmed each day in Florida. Knowing the age distribution of new cases, we can make a fairly accurate forecast of deaths to come in Florida and the rest of the country over the next two weeks.
The reason is that there is always a lag of 1-2 weeks between test confirmation and case resolution (death or recovery) so that the sharp increase in case counts seen around June 10th is just feeding into increased hospitalizations last week and death counts now and will cause them to rise into July. The projected daily death count (green triangles against the right axis in the figure below) are way below historic averages. The reason is that CFR peaked near 5% for Florida earlier this year when a lot of those sickened were older males with comorbidities but now the underlying CFR for the state is below 2% as more young and asymptomatic patients have been identified.
What we see in Florida is what is playing out in dozens of other states around the country as states reopened too quickly without regard for data or common sense. We should point out again that this Summer disaster need not play out this way. Masking, social distancing, testing, contact tracing, and selective isolation are proven techniques to limit the spread of COVID-19 and can reduce the number of unnecessary casualties in the USA.