Overestimating Death Rates: Comparing Fatality Rates of Coronavirus & the Flu

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Overestimating Death Rates: Comparing Fatality Rates of Coronavirus & the Flu
March 28, 2020 by Jonathan MS Pearce

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Fatality Rates Aren’t Fixed: They Depend on What We Do
Fundamentally, there is no such thing as “the” fatality rate for a virus. How likely people are to die from COVID-19 (just like many diseases) depends on whether they can get access to treatment.

There is no such thing as “the” death rate for a virus. It changes based on what we do.

If the medical system is able to provide adequate care — as it mostly has in South Korea, China outside of Hubei, and for cruise ship passengers in Japan — fatality rates will be lower.

But if hospitals and ICUs are suddenly swamped with cases — like in Wuhan and Italy — deaths will rise, even though the virus itself isn’t behaving any differently. Patients who need a ventilator to breathe and don’t get it have a fatality rate of 100%. [source]

The fatality rate of coronavirus is under the microsope. It appears to be anywhere between 0.5% and 3.5%. More on this in a second. This is made worse when considering the state of different healthcare systems throughout the world, giving rates anywhere between 0.6% and 5% or higher. It also depends on the “when” factor – when in the crisis you measure. Regular flu has a fatality rate of just less than 0.1%, which means that Covid-19 seems vastly more deadly.
This, and its infection rate, is what has kicked the world into action and governments into issuing lockdowns.

The problem, as many have pointed out, is that, without accurate testing, the infection rate is skewed, and so the fatality rate is skewed. The whole thing depends on knowing how many people have contracted the disease, including asymptomatic and mild sufferers. Because people are only being tested when they are pretty ill, it has been hard to get a proper sense of how many people have actually got this disease. Therefore, working out fatality rates is difficult, and the real rates are potentially wildly wrong, since we don’t know how many asymptomatic or mild sufferers there are.
The Wall Street Journal lays out this problem:

Fear of Covid-19 is based on its high estimated case fatality rate—2% to 4% of people with confirmed Covid-19 have died, according to the World Health Organization and others. So if 100 million Americans ultimately get the disease, two million to four million could die. We believe that estimate is deeply flawed. The true fatality rate is the portion of those infected who die, not the deaths from identified positive cases. The latter rate is misleading because of selection bias in testing. The degree of bias is uncertain because available data are limited. But it could make the difference between an epidemic that kills 20,000 and one that kills two million. If the number of actual infections is much larger than the number of cases—orders of magnitude larger—then the true fatality rate is much lower as well. That’s not only plausible but likely based on what we know so far.

Population samples from China, Italy, Iceland and the U.S. provide relevant evidence. On or around Jan. 31, countries sent planes to evacuate citizens from Wuhan, China. When those planes landed, the passengers were tested for Covid-19 and quarantined. After 14 days, the percentage who tested positive was 0.9%. If this was the prevalence in the greater Wuhan area on Jan. 31, then, with a population of about 20 million, greater Wuhan had 178,000 infections, about 30-fold more than the number of reported cases. The fatality rate, then, would be at least 10fold lower than estimates based on reported cases.

Next, the northeastern Italian town of Vò, near the provincial capital of Padua. On March 6, all 3,300 people of Vò were tested, and 90 were positive, a prevalence of 2.7%. Applying that prevalence to the whole province (population 955,000), which had 198 reported cases, suggests there were actually 26,000 infections at that time. That’s more than 130-fold the number of actual reported cases. Since Italy’s case fatality rate of 8% is estimated using the confirmed cases, the real fatality rate could in fact be closer to 0.06%.

In Iceland, deCode Genetics is working with the government to perform widespread testing. In a sample of nearly 2,000 entirely asymptomatic people, researchers estimated disease prevalence of just over 1%. Iceland’s first case was reported on Feb. 28, weeks behind the U.S. It’s plausible that the proportion of the U.S. population that has been infected is double, triple or even 10 times as high as the estimates from Iceland. That also implies a dramatically lower fatality rate.

The best (albeit very weak) evidence in the U.S. comes from the National Basketball Association. Between March 11 and 19, a substantial number of NBA players and teams received testing. By March 19, 10 out of 450 rostered players were positive. Since not everyone was tested, that represents a lower bound on the prevalence of 2.2%. The NBA isn’t a representative population, and contact among players might have facilitated transmission. But if we extend that lower-bound assumption to cities with NBA teams (population 45 million), we get at least 990,000 infections in the U.S. The number of cases reported on March 19 in the U.S. was 13,677, more than 72-fold lower. These numbers imply a fatality rate from Covid-19 orders of magnitude smaller than it appears.