Originally posted on April 25th, 2020 on Facebook
This one is going to be a little mathy. Several people have sent me the video titled “Dr. Erickson COVID-19 Briefing”. I’ve watched the first 12 minutes of the 52 minute video. Dr. Erickson argues that we have a large number of current cases, and that when comparing this number to deaths, he calculates the fatality rate at between 0.03 and 0.07%. This is less than the typical flu. He uses data from his home county of Kern County in California, NYC, the US, Spain, and others. Unfortunately, Dr. Erickson makes a critical error in his calculations.
For the US, he says we have 802,000 confirmed cases (around April 20th) and around 4 million tests. This would give him a positivity rate of 20% for the country. He then calculates that we then have 64 million cases in the country and only 45,000 deaths, giving us a fatality rate of 0.07%
The mistake he makes is that he assumes that tests given represents a random sampling of the population. Anyone who has tried to get a test and failed knows that not everyone who wants a test gets one. And not everyone requests a test either. Dr. Erickson has what’s called a sampling bias. You have to make sure you have a sample that represents the group you want test if you want to say anything about that group. Instead of testing the general population, Dr. Erickson is testing just people who meet the criteria for testing by the CDC or other health care body. This group is far smaller, and far more likely to have the virus than the general population. He over-estimates the number of COVID cases, by maybe 10 fold.
Several studies, some not yet published, have tested random selections of the population using PCR and antibody tests (see references 1, 2, 3, below). In those studies, fatality rates range from 0.12 – 0.7%, 2 – 23x higher than Dr. Erickson’s estimate. Also, the studies by Bendavid and Sood (2, 3) suggested that approx. 4% of the populations of Santa Clara County (San Jose) and Los Angeles were infected in early to mid April. So 96% of the population is still susceptible. At the 0.12 – 0.7 death rate, that’s 6,000 – 37,000 potential deaths for those 2 places alone. Even these studies, with fatality rates far higher than Dr. Erickson’s, have been criticized for an estimate that is too low because of sample bias (4).
We won’t really know how many people have had it until there is wide spread testing. South Korea has done extensive testing, and their fatality rate is 2.24%. This might be in the ballpark of the rate in the US.
So I have to reiterate, SARS-2 is not the average flu. In addition to being up to at least 5x more deadly, it’s also 4x more infectious. The very good news is, our efforts are paying off, and the daily rate of new cases for the US is now just 2.46%, down from a terrifying 46% on March 19th. It’s right for some living in rural areas to wonder if they can begin the process of going back to normal. Some can, but it needs to be done carefully and watchfully, with lots of testing for exposure, not just for symptoms (See my April 9th and April 22nd posts). The entire state of Minnesota plans to do just that. We can watch in real time to see how it goes for them. We don’t want another Albany, Georgia! Urban areas like coastal California and the Acela Corridor will have to wait awhile longer.
Don’t fear, but be smart!
1. Sutton et al., Universal Screening for SARS-CoV-2 in Women Admitted for Delivery. April 13, 2020. NEJM, nejm.org
2. Bendavid et al., COVID-19 Antibody Seroprevalence in Santa Clara County, California, April 11, 2020, preprint by medRxiv
3. CBS report on upcoming study
4. Experts demolish studies suggesting COVID-19 is no worse than flu
PS. If you want me to watch something later in Dr. Erickson’s video, please tell me what the time reference is. I really don’t want to watch the whole thing!