I have a strong background in statistics and epidemiology, and I am fascinated with numbers. Yes, I'm a numbers nerd and, ironically, it's a nice feature in the midst of the pandemic. These days we are bombarded with some scary numbers and projections and we hear different experts saying things that range from "it's just like a regular flu" to "the world will never be the same again". I wouldn't call myself an expert in it, just because I'm a very modest guy, but I think I'm well equipped to talk about these number and projections today and to help you understand them in a proper context.
Before we begin, I must make two disclaimers:
1. I'm a practicing physician and this blog is not a medical advice, it's an educational blog. I simply share my opinions and my knowledge. If you need medical advice, please talk to your family doctor or if you are experiencing an emergency call 911 or go to the nearest emergency room.
2. The intent of this blog is to help everyone understand the reality of this pandemic and to stay calm and rational. I don't want anyone to panic because of the statistics and projections we hear, and I don't want to minimize this serious issue.
Absolute numbers with no context
Now, when we're done with the disclaimers, we can review the statistics and crunch some numbers. First of all, I would like to point out that the statistics we hear are the scariest ones possible. Would you be scared with a statistic like 0.2% of the US population has the virus? Or 0.04% globally? Likely not, but what we hear is absolute numbers – "two and a half million cases worldwide", "750 thousand cases in US alone" followed by the number of deaths in thousands and pictures of overcrowded hospitals, exhausted ER staff and refrigerators used as mobile morgues.
I am not trying to minimize the scope of the problem – my heart is with people who have been affected by it – but I want to have this kind of data presented to me in appropriate context, so I could make rational decisions. Instead we have statistics that make our hair stand and instill deep fear and the feeling of impending doom. What I would like to do is dispelling some emerging statistical myths.
Myth #1: "It's just like a flu"
What if I told you that these numbers are not only misleading, but also are very likely to be wrong? Let's take a look. First of all, I would like to compare the COVID-19 statistics to the regular flu data. I know, it sounds like a politician talk, and I before I make this comparison, I want to say that in my educated opinion, the COVID-19 situation is much more serious that a regular flu. But let's be objective and compare the scale of this pandemic to something of the same sort, apples to apples, so to say.
I will use the US data as they are readily available. During the 2018-19 flu season in the United States there were estimated 35.5 million cases of influenza (vs slightly over 788 thousand coronavirus cases as of April 21st, 2019), with 16.5 million people going to a healthcare provider, 490 thousand hospitalizations and 34,200 deaths (comparable to the death toll in the US so far). Again, the problem is clearly there, but I hope that at this point the scare factor should have gone down a bit. Several things that make me think that the COVID-19 is still much more serious problem than the regular flu are as follows:
1. The US population is at least partially vaccinated against the flu, which slows down its spread.
2. A very high number of individuals had contracted flu already, so the herd immunity has likely formed.
3. The flu season is almost over, whereas the COVID-19 pandemic keeps spreading, so likely the numbers will keep increasing.
4. The curve has been flattened and lots of steps were taken to slow down the spread of the virus, so the numbers are lower than they could be.
So, to be completely transparent, the COVID-19 is objectively much more serious that the regular flu and I hope that I made it clear. I am a bit tired of hearing some politicians saying that it's all fear mongering. It is not, and we should not underestimate the problem.
Myths #2 and #3: The mortality rate is "3.4% or even higher" or "it's not higher than regular flu (0.1%)", respectively
We hear different mortality estimates depending on the source and there is a huge variability worldwide from less than 1% at some places to over 10% in Italy. I hear completely opposite estimates of the case fatality rate (CFR) and I would like to clarify these two misconceptions at once.
Let's start with taking a closer look at this indicator. CFR is calculated as a ratio of number of deaths from a disease and the number of confirmed cases of the disease. From what I see, likely both numbers are very biased. First of all, the number of coronavirus related deaths is likely at least slightly overestimated as in some (we don't know how many) cases people with confirmed COVID-19 die from other health issues, but are still reported as COVID-19 fatalities. It was publicly admitted by the White House task force that they are "very liberal" with their estimates and any person who dies with COVID-19 is counted as died of COVID-19. It is a very common practice in public health as in many cases it's hard to tell the difference.
At the same time, it is not the major source of bias – the real problem is that we don't know the real number of infected people. There are not enough testing kits to begin with and as practice shows the broader the testing coverage the more confirmed cases we get. For example in Iceland, where they were able to test1 more individuals than other countries did, they have 1 case per 245 citizens and in the US, which still experiences shortages of testing equipment and has to ration these tests, they have 1 case per 968 citizens. These data were obtained over a week ago, so they might have changed slightly. But still, does it mean that Iceland has 4x more cases per capita? I don't think so, most likely it means that per each confirmed case of coronavirus in the US, there are 3-4 unidentified cases. In fact, the most recent study2 reported by Dr.Ioannidis (I will review the study separately) confirms that my "guestimates" are close to reality – the number of infect people is grossly underestimated.
Accordingly, since we have an overestimation of the numerator and the gross underestimation of the denominator, the real CFR is much, much lower than the one we see in the news. We can compare the mortality rate between Iceland and the US: in the country with much higher detection of the virus the CFR is much lower - 0.6% in Iceland vs. 5.7% in the US as of April 21st, 2020. It's 10 times higher in the US and I do not think that the health care system in the US is worse than in Iceland, so it's a purely statistical phenomenon. The more people we test, the lower the mortality rate will be! In fact, it would be much closer to the mortality rate of a regular flu.
At the same time, I will stress it once again – even after all adjustments it would still be several times higher than the mortality from regular flu. I am very skeptical of the statements that "it's not higher than the flu" mortality rate – if it was the case we wouldn't have this problem, we wouldn't have such a surge in viral pneumonia deaths worldwide as we had unfortunately observed in the recent months.
My overall conclusion, supported by the numbers, is that the COVID-19 mortality rate is overestimated, but at the same time the problem is much more serious than the regular flu. I do not want to minimize the problem, but I want us to have an objective understanding of its scope and being able to respond to it rationally, not in a panic mode. I also don't want to spread the fear mongering and anxiety contagion, even though it might help flattening the curve. I want us to focus on rational steps that all of us can and should take to slow down the spread of the virus and to minimize its burden – limiting physical contacts, maintaining proper hygiene and sanitation, using personal protective equipment and several other things that we can do to help. I will talk about them in one of my next blogs, so if you don't want to miss anything, subscribe to my YouTube channel and to my newsletter and feel free to ask questions, make comments and suggestions. All interactions are welcome.
Stay safe, strong and healthy
CDC website with the influenza data:
COVID-19 Interactive map:
1. Gudbjartsson DF, Helgason A, Jonsson H, et al. Spread of SARS-CoV-2 in the Icelandic Population. New England Journal of Medicine. 2020.
2. Bendavid E, Mulaney B, Sood N, et al. COVID-19 Antibody Seroprevalence in Santa Clara County, California. medRxiv. 2020:2020.2004.2014.20062463.