epidemic

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

pnrj current events, public policy , , , , ,

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

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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 infected—slightly 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.

What do we mean by “obesity”?

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Nov 25 JDN 2458448

I thought this topic would be particularly appropriate for the week of Thanksgiving, since as a matter of public ritual, this time every year, we eat too much and don’t get enough exercise.

No doubt you have heard the term “obesity epidemic”: It’s not just used by WebMD or mainstream news; it’s also used by the American Heart Association, the Center for Disease Control, the World Health Organization, and sometimes even published in peer-reviewed journal articles.

This is kind of weird, because the formal meaning of the term “epidemic” clearly does not apply here. I feel uncomfortable going against public health officials in what is clearly their area of expertise rather than my own, but everything I’ve ever read about the official definition of the word “epidemic” requires it to be an infectious disease. You can’t “catch” obesity. Hanging out with people who are obese may slightly raise your risk of obesity, but not in the way that hanging out with people with influenza gives you influenza. It’s not caused by bacteria or viruses. Eating food touched by a fat person won’t cause you to catch the fat. Therefore, whatever else it is, this is not an epidemic. (I guess sometimes we use the term more metaphorically, “an epidemic of bankruptcies” or an “epidemic of video game consumption”; but I feel like the WHO and CDC of all people should be more careful.)

Indeed, before we decide what exactly this is, I think we should first ask ourselves a deeper question: What do we mean by “obesity”?

The standard definition of “obesity” relies upon the body mass index (BMI), a very crude measure that simply takes your body mass and divides by the square of your height. It’s easy to measure, but that’s basically its only redeeming quality.

Anyone who has studied dimensional analysis should immediately see a problem here: That isn’t a unit of density. It’s a unit of… density-length? If you take the exact same individual and scale them up by 10%, their BMI will increase by 10%. Do we really intend to say that simply being larger makes you obese, for the exact same ratios of muscle, fat, and bone?

Because of this, the taller you are, the more likely your BMI is going to register as “obese”, holding constant your actual level of health and fitness. And worldwide, average height has been increasing. This isn’t enough to account for the entire trend in rising BMI, but it reduces it substantially; average height has increased by about 10% since the 1950s, which is enough to raise our average BMI by about 2 points of the 5-point observed increase.

And of course BMI doesn’t say anything about your actual ratios of fat and muscle; all it says is how many total kilograms are in your body. As a result, there is a systematic bias against athletes in the calculation of BMI—and any health measure that is biased against athletes is clearly doing something wrong. All those doctors telling us to exercise more may not realize it, but if we actually took their advice, our BMIs would very likely get higher, not lower—especially for men, especially for strength-building exercise.

It’s also quite clear that our standards for “healthy weight” are distorted by social norms. Feminists have been talking about this for years; most women will never look like supermodels no matter how much weight they lose—and eating disorders are much more dangerous than being even 50 pounds overweight. We’re starting to figure out that similar principles hold for men: A six-pack of abs doesn’t actually mean you’re healthy; it means you are dangerously depleted of fatty acids.

To compensate for this, it seems like the most sensible methodology would be to figure out empirically what sort of weight is most strongly correlated with good health and long lifespan—what BMI maximizes your expected QALY.

You might think that this is what public health officials did when defining what is currently categorized as “normal weight”—but you would be wrong. They used social norms and general intuition, and as a result, our standards for “normal weight” are systematically miscalibrated.

In fact, the empirical evidence is quite clear: The people with the highest expected QALY are those who are classified as “overweight”, with BMI between 25 and 30. Those of “normal weight” (20 to 25) fare slightly worse, followed by those classified as “obese class I” (30 to 35)—but we don’t actually see large effects until either “underweight” (18.5-20) or “obese class II” (35 to 40). And the really severe drops in life and health expectancy don’t happen until “obese class III” (>40); and we see the same severe drops at “very underweight” (<18.5).
With that in mind, consider that the global average BMI increased from 21.7 in men and 21.4 in women in 1975 to 24.2 in men and 24.4 in women in 2014. That is, the world average increased from the low end of “normal weight” which is actually too light, to the high end of “normal weight” which is probably optimal. The global prevalence of “morbid obesity”, the kind that actually has severely detrimental effects on health, is only 0.64% in men and 1.6% in men. Even including “severe obesity”, the kind that has a noticeable but not dramatic effect on health, is only 2.3% in men and 5.0% in women. That’s your epidemic? Reporting often says things like “2/3 of American adults are overweight or obese”; but all that “overweight” proportion should be utterly disregarded, since it is beneficial to health. The actual prevalence of obesity in the US—even including class I obesity which is not very harmful—is less than 40%.

If obesity were the health crisis it were made out to be, we should expect that global life expectancy is decreasing, or at the very least not increasing. On the contrary, it is rapidly increasing: In 1955, global life expectancy was only 55 years, while it is now over 70.

Worldwide, the countries with the highest obesity rates are those with the longest life expectancy, because both of these things are strongly correlated with high levels of economic development. But it may not just be that: Smoking reduces obesity while also reducing lifespan, and a lot of those countries with very high obesity (including the US) have very low rates of smoking.

There’s some evidence that within the set of rich, highly-developed countries, obesity rates are positively correlated with lower life expectancy, but these effects are much smaller than the effects of high development itself. Going from the highest obesity in the world (the US, of course) to the lowest among all highly-developed countries (Japan) requires reducing the obesity rate by 34 percentage points but only increases life expectancy by about 5 years. You’d get the same increase by raising overall economic development from the level of Turkey to the level of Greece, about 10 points on the 100-point HDI scale.

 

Now, am I saying that we should all be 400 pounds? No, there does come a point where excess weight is clearly detrimental to health. But this threshold is considerably higher than you have probably been led to believe. If you are 15 or 20 pounds “overweight” by what our society (or even your doctor!) tells you, you are probably actually at the optimal weight for your body type. If you are 30 or 40 pounds “overweight”, you may want to try to lose some weight, but don’t make yourself suffer to achieve it. Only if you are 50 pounds or more “overweight” should you really be considering drastic action. If you do try to lose weight, be realistic about your goal: Losing 5% to 10% of your initial weight is a roaring success.

There are also reasons to be particularly concerned about obesity and lack of exercise in children, which is why Michelle Obama’s “Let’s Move!” campaign was a good thing.

And yes, exercise more! Don’t do it to try to lose weight (exercise does not actually cause much weight loss). Just do it. Exercise has so many health benefits it’s honestly kind of ridiculous.

But why am I complaining about this, anyway? Even if we cause some people to worry more about eating less than is strictly necessary, what’s the harm in that? At least we’re getting people to exercise, and Thanksgiving was already ruined by politics anyway.

Well, here’s the thing: I don’t think this obesity panic is actually making us any less obese.

The United States is the most obese country in the world—and you can’t so much as call up Facebook or step into a subway car in the US without someone telling you that you’re too fat and you need to lose weight. The people who really are obese and may need medical help losing weight are the ones most likely to be publicly shamed and harassed for their weight—and there’s no evidence that this actually does anything to reduce their weight. People who experience shaming and harassment for their weight are actually less likely to achieve sustained weight loss.

Teenagers—both boys and girls—who are perceived to be “overweight” are at substantially elevated risk of depression and suicide. People who more fully internalize feelings of shame about their weight have higher blood pressure and higher triglicerides, though once you control for other factors the effect is not huge. There’s even evidence that fat shaming by medical professionals leads to worse treatment outcomes among obese patients.

If we want to actually reduce obesity—and this makes sense, at least for the upper-tail obesity of BMI above 35—then we should be looking at what sort of interventions are actually effective at doing that. Medicine has an important role to play of course, but I actually think economics might be stronger here (though I suppose I would, wouldn’t I?).

Number 1: Stop subsidizing meat and feed grains. There is now quite clear evidence that direct and indirect government subsidies for meat production are a contributing factor in our high fat consumption and thus high obesity rate, though obviously other factors matter too. If you’re worried about farmers, subsidize vegetables instead, or pay for active labor market programs that will train those farmers to work in new industries. This thing we do where we try to save the job instead of the worker is fundamentally idiotic and destructive. Jobs are supposed to be destroyed; that’s what technological improvement is. If you stop destroying jobs, you will stop economic growth.

Number 2: Restrict advertising of high-sugar, high-fat foods, especially to children. Food advertising is particularly effective, because it draws on such primal impulses, and children are particularly vulnerable (as the APA has publicly reported on, including specifically for food advertising). Corporations like McDonald’s and Kellogg’s know quite well what they’re doing when they advertise high-fat, high-sugar foods to kids and get them into the habit of eating them early.

Number 3: Find policies to promote exercise. Despite its small effects on weight loss, exercise has enormous effects on health. Indeed, the fact that people who successfully lose weight show long-term benefits even if they put the weight back on suggests to me that really what they gained was a habit of exercise. We need to find ways to integrate exercise into our daily lives more. The one big thing that our ancestors did do better than we do is constantly exercise—be it hunting, gathering, or farming. Standing desks and treadmill desks may seem weird, but there is evidence that they actually improve health. Right now they are quite expensive, so most people don’t buy them. If we subsidized them, they would be cheaper; if they were cheaper, more people would buy them; if more people bought them, they would seem less weird. Eventually, it could become normative to walk on a treadmill while you work and sitting might seem weird. Even a quite large subsidy could be worthwhile: say we had to spend $500 per person per year to buy every single adult a treadmill desk each year. That comes to about $80 billion per year, which is less than one fourth what we’re currently spending on diabetes or heart disease, so we’d break even if we simply managed to reduce those two conditions by 13%. Add in all the other benefits for depression, chronic pain, sleep, sexual function, and so on, and the quality of life improvement could be quite substantial.