How should we update our priors on COVID-10?
I want to think about how two pieces of news should change my thinking about COVID-19. (Warning: I have no expertise in medicine or public health, and you have no reason to take my thoughts seriously – but you knew that already.)
A new serological study in Santa Clara county (discussed by Kevin Drum here) suggests that far more people have been infected with COVID-19 than researchers had previously believed. This is only one study and full of uncertainties, but it suggests that the infection fatality rate of COVID-19 (the chance that you die if you get the virus) may be much lower than was previously believed. The authors suggest an IFR of .12% to .2%. The Imperial College study, in comparison, used a rate of .9%.
It is tempting to say that a lower infection fatality rate is a good thing: COVID-19 is less deadly than we thought. I’m not sure this is right. The fact that many more people have had the disease than we previously believed will not only affect our estimate of the infection fatality rate, it will also lead us to revise our estimates of other critical parameters. For example, it suggests that COVID-19 is much more contagious than we previously thought and that the rate of asymptomatic infections is higher than we believed.
Higher rates of contagion and asymptomatic infection are both troubling. Think about it this way. Your chance of dying from COVID-19 depends on the probability that you die if you get infected times the probability that you get infected. The new study suggests that the first number is lower than we thought, but the second number is higher. I don’t know enough about the dynamics of the SIR model to know if this is a good tradeoff, but it’s not clear that it is: Ebola had a very high fatality rate but a very low transmission rate, and we would clearly be better off with an easily contained Ebola epidemic than with COVID-19. Higher asymptomatic transmission will make it much more difficult to control the spread of the disease without prolonged social distancing or massive testing.
Second, a piece by Matt Stieb in New York Magazine reminds us that death is not the only way COVID-19 harms us. Serious long-term health impacts from COVID-19 infection – kidney and liver disease, heart and lung disease – may turn out to be relatively common among those who develop serious illness. In addition to the life long suffering this will cause, it is conceivable that the long-term loss of life-years among people who survive initial infection with COVID-19 will exceed the loss of life-years due to immediate fatalities. There may also turn out to be negative health consequences for people with less severe illness. And the immediate suffering caused by the disease is often severe as well.
I don’t have a lot of confidence in this analysis, but overall, I’d say the news of the day raises my estimate of the likely health impact of the epidemic. Of course, your mileage could easily vary. What this means for policy is a separate question.
We know nothing. Consequent the lack of adequate testing, we know nothing.
This is the cardinal sin of the Nation’s response.
Last I heard they were still evaluating the immunity tests for accuracy.
Assuming this test is accurate, even the high end (4%) is a very small number if you are looking for herd immunity. If what we are seeing represents a far wider spread with more mild or asymptomatic cases, it is still killing thousands of people in just two months. Add the possibly permanent damage to those who survive severe cases, and it really isn’t something to be glad about.
JaneE: the paper has an interesting discussion of the sensitivity of the test. Worth a read.
Looking at the test paper, the sampling methodology is the most problematic part. Since subjects volunteered for the test, it would be likely that those who suspected they had the virus would be much more likely to opt-in. There is also a false positive rate of around 0.5% and a false negative rate of 12-40%.
A more comprehensive sampling that doesn’t run into the opt-in issue is the testing done on the USS Roosevelt.
https://www.reuters.com/article/us-health-coronavirus-usa-military-sympt-idUSKCN21Y2GB
With 94% of the crew tested, 660 tested positive out of 4,800. That can’t be extrapolated to other sites, but the testing found that 60% were asymptomatic. Unfortunately, we still can’t extrapolate from that number since we don’t have a handle on what percentage of symptomatic patients in the population get tested.
My point with all of this is that we still don’t know what is going on with this outbreak. And unfortunately, much of the information we have is of poor quality and we need to be careful about accepting it at face value.
Thanks for the post, Michael.
Having served on CVA-N 65, I can relate. Have you seen any similar reports on the Charles DeGaulle?
Anecdotal but indicative.
My brother in law is a policeman in the city of Philadelphia. He has shown symptoms of fever and loss of smell and taste.
Ordered home to wait for a call from the hospital to come and get tested.
Four days and counting.