Fear not to “overreact”

Mar 29 JDN 2458938

It could be given as a story problem in an algebra class, if you didn’t mind terrifying your students:

A virus spreads exponentially, so that the population infected doubles every two days. Currently 10,000 people are infected. How long will it be until 300,000 are infected? Until 10,000,000 are infected? Until 600,000,000 are infected?

The answers:

300,000/10,000 is about 32 = 2^5, so it will take 5 doublings, or 10 days.

10,000,000/10,000 is about 1024=2^10, so it will take 10 doublings, or 20 days.

600,000,000/10,000 is about 64*1024=2^6*2^10, so it will take 16 doublings, or 32 days.

This is the approximate rate at which COVID-19 spreads if uncontrolled.

Fortunately it is not completely uncontrolled; there were about 10,000 confirmed infections on January 30, and there are now about 300,000 as of March 22. This is about 50 days, so the daily growth rate has averaged about 7%. On the other hand, this is probably a substantial underestimate, because testing remains very poor, particularly here in the US.

Yet the truth is, we don’t know how bad COVID-19 is going to get. Some estimates suggest it may be nearly as bad as the 1918 flu pandemic; others say it may not be much worse than H1N1. Perhaps all this social distancing and quarantine is an overreaction? Perhaps the damage from closing all the schools and restaurants will actually be worse than the damage from the virus itself?

Yes, it’s possible we are overreacting. But we really shouldn’t be too worried about this possibility.

This is because the costs here are highly asymmetric. Overreaction has a moderate, fairly predictable cost. Underreaction could be utterly catastrophic. If we overreact, we waste a quarter or two of productivity, and then everything returns to normal. If we underreact, millions of people die.

This is what it means to err on the side of caution: If we are not 90% sure that we are overreacting, then we should be doing more. We should be fed up with the quarantine procedures and nearly certain that they are not all necessary. That means we are doing the right thing.

Indeed, the really terrifying thing is that we may already have underreacted. These graphs of what will happen under various scenarios really don’t look good:

pandemic_graph

But there may still be a chance to react adequately. The advice for most of us seems almost too simple: Stay home. Wash your hands.

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.