The USA COVID-19 “Case Fatality Rate” has held steady between 1.2% and 1.5% for almost three weeks.
That number will decline significantly when massive wide scale USA testing begins to capture the huge percentage of non-infected Americans in the data.
Case Fatality rate is only useful under two conditions:
1) where people who are going to die from the disease do so nearly immediately upon being detected as having the disease.
2) After the outbreak, or at least the cohort, has completely ended.
Or else what you are really measuring is speed of spread. As long as the speed of spread is growing consistently, the case fatality rate will be relatively stable. When the disease begins to limit, the case fatality rate will rise to it’s actual ratio.
Because of the extreme length between symptom/detection and death, and then a further length to recovery, there is a sort of flattened ‘S’ shape added to the also-flattened upside-down Bell-curve of the case fatality rate during the outbreak.
“Jordan Schachtel, a national security writer, said COVID Act Now’s modeling comes from one team based at Imperial College London that is not only highly scrutinized, but has a track record of bad predictions,” Osburn said.
Jessica Hamzelou at New Scientist explained how Chen Shen at the New England Complex Systems Institute, a research group in Cambridge, Massachusetts, found flaws and “incorrect assumptions” in the formulas.
Even COVID Act Now has started acknowledging “limitations,” including that “many” original numbers “are based on early estimates that are likely to be wrong” and “demographics, populations and hospital bed counts are outdated.”
In a dynamic medical event, Case Fatality Rate and Secondary Infection Rate are the only helpful numbers we have.
After two months of USA COVID-19 data, both of those rates have an obvious trend - stable to slightly down.
In medically advanced countries, initial testing focuses on high risk groups - those with known exposure or obvious symptoms.
Germany is the only exception - their private labs have conducted millions of tests, and their CFR is the lowest in the world for a large country - 0.5%.
Here in Washington state, our Secondary Infection Rate has been steady between 6.5% and 7.5% for more than two weeks.
In a normal influenza season, that number would be 30% to 40%.
Washington is about to get a deluge of new test reports. Lab reports increased by 10X a couple days ago, and it crashed our reporting network.