We still don’t know the fatality rate of COVID-19

May 10 JDN2458978

You’d think after being in this pandemic for several weeks we would now have a clear idea of the fatality rate of the virus. Unfortunately, this is not the case.

The problem is that what we can track really doesn’t tell us what we need to know.

What we can track is how many people have tested positive versus how many people have died. As of this writing, 247,000 people have died and 3,504,000 have tested positive. If this were the true fatality rate, it would be horrifying: A death rate of 7% is clearly in excess of even the 1918 influenza pandemic.

Fortunately, this is almost certainly an overestimate. But it’s actually possible for it to be an underestimate, and here’s why: A lot of those people who currently have the virus could still die.

We really shouldn’t be dividing (total deaths)/(total confirmed infections). We should be dividing (total deaths)/(total deaths + total recoveries). If people haven’t recovered yet, it’s too soon to say whether they will live.

On that basis, this begins to look more like an ancient plague: The number of recoveries is only about four times the number of deaths, which would be a staggering fatality rate of 20%.

But as I said, it’s far more likely that this is an overestimate, because we don’t actually know how many people have been infected. We only know how many people have been infected and gotten tested. A large proportion have never been tested; many of these were simply asymptomatic.
We know this because of the few cases we have of rigorous testing of a whole population, such as the passengers on this cruise liner bound for Antarctica. On that cruise liner, 6 were hospitalized, but 128 tested positive for the virus. This means that the number of asymptomatic infections was twenty times that of the number of symptomatic infections.

There have been several studies attempting to determine what proportion of infections are asymptomatic, because this knowledge is so vital. Unfortunately the results are wildly inconsistent. They seem to range from 5% asymptomatic and 95% symptomatic to 95% asymptomatic and 5% symptomatic. The figure I find most plausible is about 80%: This means that the number of asymptomatic infected is about four times that of the number of symptomatic infected.

This means that the true calculation we should be doing actually looks like this: (total deaths)/(total deaths + total recoveries + total asymptomatic).

The number of deaths seems to be about one fourth the number of recoveries. But when you add the fact that four times as many who get infected are asymptomatic, things don’t look quite so bad. This yields an overall fatality rate of about 4%. This is still very high, and absolutely comparable to the 1918 influenza pandemic.

But the truth is, we just don’t know. South Korea’s fatality rate was only 0.7%, which would be a really bad flu season but nothing catastrophic. (A typical flu has a fatality rate of about 0.1%.) On the (deaths)/(deaths + recoveries) basis, it looks almost as bad as the Black Death.

With so much uncertainty, there’s really only one option: Prepare for the worst-case scenario. Assume that the real death rate is massive, and implement lockdown measures until you can confirm that it isn’t.

Ancient plagues, modern pandemics

Mar 1 JDN 2458917

The coronavirus epidemic continues; though it originated in Wuhan province, the virus has now been confirmed in places as far-flung as Italy, Brazil, and Mexico. So far, about 90,000 people have caught it, and about 3,000 have died, mostly in China.

There are legitimate reasons to be concerned about this epidemic: Like influenza, coronavirus spreads quickly, and can be carried without symptoms, yet unlike influenza, it has a very high rate of complications, causing hospitalization as often as 10% of the time and death as often as 2%. There’s a lot of uncertainty about these numbers, because it’s difficult to know exactly how many people are infected but either have no symptoms or have symptoms that can be confused with other diseases. But we do have reason to believe that coronavirus is much deadlier for those infected than influenza: Influenza spreads so widely that it kills about 300,000 people every year, but this is only 0.1% of the people infected.

And yet, despite our complex interwoven network of international trade that sends people and goods all around the world, our era is probably the safest in history in terms of the risk of infectious disease.

Partly this is technology: Especially for bacterial infections, we have highly effective treatments that our forebears lacked. But for most viral infections we actually don’t have very effective treatments—which means that technology per se is not the real hero here.

Vaccination is a major part of the answer: Vaccines have effectively eradicated polio and smallpox, and would probably be on track to eliminate measles and rubella if not for dangerous anti-vaccination ideology. But even with no vaccine against coronavirus (yet) and not very effective vaccines against influenza, still the death rates from these viruses are nowhere near those of ancient plagues.

The Black Death killed something like 40% of Europe’s entire population. The Plague of Justinian killed as many as 20% of the entire world’s population. This is a staggeringly large death rate compared to a modern pandemic, in which even a 2% death rate would be considered a total catastrophe.

Even the 1918 influenza pandemic, which killed more than all the battle deaths in World War I combined, wasn’t as terrible as an ancient plague; it killed about 2% of the infected population. And when a very similar influenza virus appeared in 2009, how many people did it kill? About 400,000 people, roughly 0.1% of those infectedslightly worse than the average flu season. That’s how much better our public health has gotten in the last century alone.

Remember SARS, a previous viral pandemic that also emerged in China? It only killed 774 people, in a year in which over 300,000 died of influenza.

Sanitation is probably the most important factor: Certainly sanitation was far worse in ancient times. Today almost everyone routinely showers and washes their hands, which makes a big difference—but it’s notable that widespread bathing didn’t save the Romans from the Plague of Justinian.

I think it’s underappreciated just how much better our communication and quarantine procedures are today than they once were. In ancient times, the only way you heard about a plague was a live messenger carrying the news—and that messenger might well be already carrying the virus. Today, an epidemic in China becomes immediate news around the world. This means that people prepare—they avoid travel, they stock up on food, they become more diligent about keeping clean. And perhaps even more important than the preparation by individual people is the preparation by institutions: Governments, hospitals, research labs. We can see the pandemic coming and be ready to respond weeks or even months before it hits us.

So yes, do wash your hands regularly. Wash for at least 20 seconds, which will definitely feel like a long time if you haven’t made it a habit—but it does make a difference. Try to avoid travel for awhile. Stock up on food and water in case you need to be quarantined. Follow whatever instructions public health officials give as the pandemic progresses. But you don’t need to panic: We’ve got this under control. That Horseman of the Apocalypse is dead; and fear not, Famine and War are next. I’m afraid Death himself will probably be awhile, though.

Influenza vaccination, herd immunity, and the Tragedy of the Commons

Dec 24, JDN 2458112

Usually around this time of year I do a sort of “Christmas special” blog post, something about holidays or gifts. But this year I have a rather different seasonal idea in mind. It’s not just the holiday season; it’s also flu season.

Each year, influenza kills over 56,000 people in the US, and between 300,000 and 600,000 people worldwide, mostly in the winter months. And yet, in any given year, only about 40% of adults and 60% of children get the flu vaccine.

The reason for this should be obvious to any student of economics: It’s a Tragedy of the Commons. If enough people got vaccinated that we attained reliable herd immunity (which would take about 90%), then almost nobody would get influenza, and the death rate would plummet. But for any given individual, the vaccine is actually not all that effective. Your risk of getting the flu only drops by about half if you receive the vaccine. The effectiveness is particularly low among the elderly, who are also at the highest risk for serious complications due to influenza.

Thus, for any given individual, the incentive to get vaccinated isn’t all that strong, even though society as a whole would be much better off if we all got vaccinated. Your probability of suffering serious complications from influenza is quite low, and wouldn’t be reduced all that much if you got the vaccine; so even though flu vaccines aren’t that costly in terms of time, money, discomfort, and inconvenience, the cost is just high enough that a lot of us don’t bother to get the shot each year.

On an individual level, my advice is simple: Go get a flu shot. Don’t do it just for yourself; do it for everyone around you. You are protecting the most vulnerable people in our society.

But if we really want everyone to get vaccinated, we need a policy response. I can think of two policies that might work, which can be broadly called a “stick” and a “carrot”.

The “stick” approach would be to make vaccination mandatory, as it already is for many childhood vaccines. Some sort of penalty would have to be introduced, but that’s not the real challenge. The real challenge would be how to actually enforce that penalty: How do we tell who is vaccinated and who isn’t?

When schools make vaccination mandatory, they require vaccination records for admission. It would be simple enough to add annual flu vaccines to the list of required shots for high schools and colleges (though no doubt the anti-vax crowd would make a ruckus). But can you make vaccination mandatory for work? That seems like a much larger violation of civil liberties. Alternatively, we could require that people submit medical records with their tax returns to avoid a tax penalty—but the privacy violations there are quite substantial as well.

Hence, I would favor the “carrot” approach: Use government subsidies to provide a positive incentive for vaccination. Don’t simply make vaccination free; actually pay people to get vaccinated. Make the subsidy larger than the actual cost of the shots, and require that the doctors and pharmacies administering them remit the extra to the customers. Something like $20 per shot ought to do it; since the cost of the shots is also around $20, then vaccinating the full 300 million people of the United States every year would cost about $12 billion; this is less than the estimated economic cost of influenza, so it would essentially pay for itself.

$20 isn’t a lot of money for most people; but then, like I said, the time and inconvenience of a flu shot aren’t that large either. There have been moderately successful (but expensive) programs incentivizing doctors to perform vaccinations, but that’s stupid; frankly I’m amazed it worked at all. It’s patients who need incentivized. Doctors will give you a flu shot if you ask them. The problem is that most people don’t ask.

Do this, and we could potentially save tens of thousands of lives every year, for essentially zero net cost. And that sounds to me like a Christmas wish worth making.