Corona-Oh-Nah-Nah!
This post will either go down in my blog history as one of the stupidest dumbest paranoid analysis of the numbers behind COVID-19 fatality rates, or (hopefully) end up as a thoughtful neutral analysis of the facts as they stand currently. With the recent coronavirus pandemic, there have been a lot of comparisons made in the media with the flu, and a lot of discussions had about the severity of this virus. Especially about its mortality rate. Since, I’m currently funemployed and got nothing better to do while in quarantine, I felt the need to chime in on the topic as well :)
Mortality vs. Case Fatality
First, we need to understand the metric we are discussing here. The Center for Disease Control (CDC) as well as the World Health Organization (WHO) both define mortality rate as the number of people dying from an infection divided by the total number of people infected.
Mortality Rate = Number of Deaths / Number of Infected.
For COVID-19, or more precisely, for SARS-nCOV2, the WHO estimates mortality rate for the virus to be around 3.4% (and climbing). The CDC estimates it to be around 1 - 2%. And everyone in the media have been comparing it with Influenza, which has a mortality rate of about 0.1%, and claiming that this Coronavirus infection is 10 - 15x as deadly.
For a pessimistic outlook, talk to any statistician (or me) and they will point out that the numerator isn’t fully determined as you are dividing deaths from just closed cases over the total number of cases including both active and closed cases. And just based on that, assuming active cases close with the same percentage of fatalities, you would end up with double the numerator and around a 7% mortality rate by WHO’s measure. Of course, that is assuming that new cases are growing linearly. But we know, we are on an exponential curve up… so, this metric will in fact land somewhere higher.
For instance, consider a hypothetical scenario where an epidemic lasts 20 weeks, and the average duration from infection to recovery or death is around 4 weeks. Assuming a 50% mortality rate, the weekly metrics for deaths and new cases would look something like the following:
In the graph above, red represents the count of new infections, and blue represents the number of deaths per week. And, the cumulative graph would look like this:
If you calculate the mortality rate the way the WHO and CDC calculate today, then up until week 4, it would be 0%, and it will always be less than the true mortality rate of 50% slowly inching it’s way up to the true value at the end of the epidemic. This is why the WHO’s 3.4% and CDC’s 1-2% estimates are artificially optimistic. Sure, they sound nicer to our ears, but it’s only gonna get worse. Unless of course, we can find a vaccine or a cure before the bell curve peaks, which is highly doubtful.
For an optimistic outlook, talk to any doctor, and they will correctly point out that these estimates are meaningless as we don’t know how big the denominator is, because we aren’t testing everyone for the virus, and only test those with severe symptoms. So far, South Korea and the Diamond Princess Cruise are the only places where they tested people regardless of whether or not they showed symptoms, and thus those populations provide a more accurate estimate of what the mortality rate will be for the virus. And in those populations, the mortality rate was shown to be around 0.9%.
Those populations also showed that 82% of the infected either were asymptomatic (i.e, showed no symptoms) or were mildly symptomatic (i.e, a cold, or very mild fever, or a sore throat) and the symptoms went away.
This is in stark contrast to Influenza, where if you contract the virus, then you end up being symptomatic. And, this makes comparing mortality rates between the two diseases ever more meaningless. If I catch the flu, I’m gonna need hospitalization, and the 0.1% probability of dying from it applies to me. If I catch nCoV2, neither the 3.4% nor the 0.9% applies to me. If I’m over 80, then 21.9% applies to me. If I’m young and asymptomatic, almost 0% applies to me. But if I’m symptomatic enough to be admitted to the hospital, then my prognosis depends on a much smaller denominator containing just the population of those infected and had to be hospitalized. And this is where the Case Fatality Rate/Ratio (CFR) applies to me.
Case Fatality Rate
CFR = Number of Deaths / Number of Hospitalized Patients.
For Influenza, this is almost synonymous with the mortality rate. Because, if you catch the virus, then you are going to end up with the flu, and need to be hospitalized. Thus total number infected approximately equals the total number hospitalized.
But for Coronavirus, this would be vastly different from mortality rate as the number that need hospitalization is only around 17% of those infected. And since we can assume that if you are severely symptomatic, then you would end up hospitalized (similar to the flu), you can get at this number by looking at the closed cases thus far. And the numbers thus far paint a much direr picture than the 10-15x comparisons around the mortality rates.
While the flu has a CFR of around 0.1% (the same as its mortality rate), COVID-19′s CFR is around 12% and growing. (When I started writing this post, it was around 11%, and by the time I’m done writing it, it’s at 14%… Go figure! I think it’s because of the systemic failure with the Italian Healthcare System). This is about 100x that for Influenza. While this is alarming, we need to remember that while the flu affects everyone almost uniformly regardless of age, COVID-19 is especially lethal to the elderly. And a majority of those that require hospitalization are elderly and thus the numbers will get skewed towards the 21.9% mortality rate for above 80-somethings than the 0.2% mortality rate for the below 20s. And the elderly are already filling up our hospital beds, where they are most likely to contract it as well as get tested for it. So, there is definitely a bias in the overall CFR towards that of the elderly.
If you’re like me, you might think “I’m close to 40, how does this CFR affect me?” It is still worth noting that the virus is much more deadlier than the flu, and affects older population more severely because of co-morbid conditions. But it doesn’t affect old people exclusively. It also affects those with heart and pulmonary diseases, those with cancer, as well as those with diabetes more adversely than others. A lot of these conditions arise with old age. But, they also arise with obesity. And in the US, where a majority of the population is now overweight or obese, we don’t know how these conditions will affect the case outcomes for this disease. Of course, it also affects fit young people as well (I know of one 33 year old personally that had to be hospitalized for a week).
So, what do we do now?
Take this sh** seriously. Avoid contracting it as much as possible. Don’t take social distancing lightly, and be extra careful about visiting your parents / grandparents. Facetime/Zoom/Duo/WhatsApp your family. Buy them groceries and leave it at their doorstep to show that you care. But, please don’t hug and KOD your parents.
Most importantly, if you have a fever, or sore throat, DO NOT rush to the ER!!! At least, not until your symptoms turn out to be severe and you really need in-patient care, because:
1. If you have COVID-19, you are most likely to spread it to others in the ER unnecessarily, when you are just mildly symptomatic and don’t need to be hospitalized.
2. If your symptoms are not due to COVID, you are more likely to contract the virus in the ER.
You are most likely better off waiting for your symptoms to wean off while quarantining yourself at home. Also, you can’t create videos like this at the hospital… So, stay home! Stay safe! Stay creative! :)