I follow a Twitter account called “Underwhelming Facts” that tweets out facts that are really obvious. Such as: “empty wine bottles weigh less than full ones,” and “TAB is an anagram of BAT.” Wow.

Today’s IFOD may seem like its an underwhelming fact but I think it’s an important concept to keep in mind. Here it is:

A very large number times a very small number is usually a big number.

Here’s an example:

You stop at a gas station and fill your car with gasoline. As you remove the nozzle, even though you are careful, a few drops of gas fall onto the ground. Seems like no big deal – it’s just a few drops – and it happens to everyone. But, take those few drops and times it by hundreds of millions of people dropping just a few drops each time they get gas and it really adds up. A 2014 study out of Johns Hopkins found that the amount of gasoline spilled by people putting gas in their cars is about 1,500 liters per gas station per decade. There are 111,200 gas stations in the U.S. If you do the math, that means about 4.4 million gallons of gas are spilled by consumers at gas stations each year. Wow, that’s like an Exxon Valdez spill about every 2.5 years spread across local gas stations. Thus, a very big number (hundreds of millions of gas fills) times a very small number (a few drops) is a big number (millions of gallons).

The Great Influenza of 1918

Paradoxically, the epidemics that are the biggest killers usually have relatively low fatality rates but are highly contagious. Lots of people get infected, but only a small percentage die. But, a small percentage of a highly contagious disease is still a lot of death. An estimated 50 – 100 million people died of the Great Influenza even though the fatality rate was only about 2.5% because it was highly contagious and about 1/3rd of the world’s population was infected. That large number, 1/3rd of the world population, times the small fatality rate resulted in a large absolute number of deaths.

Covid-19

The same concept applies to the current pandemic: it is very contagious but has a low fatality rate which is leading to a large absolute number of deaths.

The fatality rate of Covid-19 is hard to pin down because there is some uncertainty about the exact number of Covid deaths (the numerator) as well as the number of people infected (the denominator). Also, the fatality rate varies by country, age, and race, among other factors. According to a report in Nature, the Infection Fatality Rate (IFR) is probably 0.5% – 1.0%, and the WHO recently announced that the IFR is 0.6%. Note that the IFR takes into account those people infected but not diagnosed, including asymptomatic cases.

Even though the fatality rate is low, there are potentially a lot of people who will get infected, and a very large number times a very small number is still a big number. At a 0.6% IFR, if everyone in the U.S. were to get infected then about 2 million people would die. On a worldwide basis that would equate to about 50 million deaths.

So, Covid-19 is simultaneously “not that bad” (less than 1% fatality rate) and “horrible” (over 500,000 deaths worldwide and counting).