As it turns out other people than I are also doing back-of-the-envelope calculations about COVID-19 so you don’t just have to take my word for it. Over at Bloomberg Justin Fox does it and comes up with some observations:
These fatality rates can change a lot depending on time and place and access to treatment. The Covid-19 rate is obviously a moving target, so I’ve included both the 3.4% worldwide mortality rate reported this week by the World Health Organization and the 1% estimate from a study released Feb. 10 by the MRC Centre for Global Infectious Disease Analysis at Imperial College London that factored in probable unreported cases. The authors of that study also said that, given the information available at the time, they were 95% confident the correct fatality rate was somewhere between 0.5% and 4%. Gates used the 1% estimate in his article, and when I ran it by Caroline Buckee, an actual professional epidemiologist who is a professor at Harvard’s T.H. Chan School of Public Health, she termed it “reasonable.â€
In a context that includes Ebola and MERS, the Covid-19 death rates are much closer to those of the flu, and it’s understandable why people find the comparison reassuring. Compare Covid-19 with just the flu, though, and it becomes clear how different they are.
The 61,099 flu-related deaths in the U.S. during the severe flu season of 2017-2018 amounted to 0.14% of the estimated 44.8 million cases of influenza-like illness. There were also an estimated flu-related 808,129 hospitalizations, for a rate of 1.8%. Assume a Covid-19 outbreak of similar size in the U.S., multiply the death and hospitalization estimates by five or 10, and you get some really scary numbers: 300,000 to 600,000 deaths, and 4 million to 8 million hospitalizations in a country that has 924,107 staffed hospital beds. Multiply by 40 and, well, forget about it. Also, death rates would go higher if the hospital system is overwhelmed, as happened in the Chinese province of Hubei where Covid-19’s spread began and seems to be happening in Iran now. That’s one reason that slowing the spread is important even if it turns out the disease can’t be stopped.
Could Covid-19 really spread as widely as the flu? If allowed to, sure. The standard metric for infectiousness is what’s called the reproduction number, or R0. It is usually pronounced “R naught,†and the zero after the R should be rendered in subscript, but it’s a simple enough concept. An R0 of one means each person with the disease can be expected to infect one more person. If the number dips below one, the disease will peter out. If it gets much above one, the disease can spread rapidly.
and
The numbers also seem to indicate that Covid-19 is a lot more contagious than the seasonal flu. Average R0 isn’t the whole story, though. Why all the worry about MERS, for example, which with an R0 below one shouldn’t spread at all? Well, it’s extremely deadly, its R0 can rise above one in certain environments, among them hospitals, and … you can catch it from your camel.
There are also some very nice graphs in the article if you’re interested in graphs.
Let’s make a few guesses and play with some numbers. About a third of our entire species caught Spanish flu back in 1918 so let’s use that number as a WAG. Roughly a third of 7 billion people with a mortality rate between .1% and 3% gives us between 2 million and 70 million deaths.
Since I’m over 70 I can’t take the claims that only old people are dying with the nonchalance or even outright glee that some are. Considering the U. S. alone, the numbers above suggest a number of hospitalizations and deaths that are quite likely to overwhelm our health care system and legal system and might even overwhelm our economic system.
I’m also skeptical about those claims. Italy’s population pyramid might explain its higher death rate from COVID-19 but the reports from Iran and China don’t seem to comport with their population pyramids. And then there’s the question of just how much trust we can place in the reports that China is making? There have been claims emanating from Chinese sources that the outbreak in China has been much worse than the Chinese authorities have claimed and that they’re flat out lying that it’s under control. I’ll allow that those claims may be from interested parties but IMO the reality is that we just don’t know.