How to Make COVID-19 Evolve to Become Less Dangerous

Donald Trump says that even without a vaccine, COVID-19 will eventually fade away. And amazingly, the science says he might be right…though not if we follow his plan for reopening the country.

The science in question is evolutionary virology.

It says is that under certain circumstances viruses will evolve into less virulent forms. In fact, this might even be what happened to the 1918 Spanish Flu…though not until after it killed tens of millions of people.

Let me explain.

In order to be an evolutionarily successful, virus can’t just infect one person, they have to jump from one person to another. They can do that by making us cough, giving us diarrhea that contaminates other people’s food or water, or giving us sores that shed virus particles onto anyone or anyone we touch.

I.e., they make us sick.

But if they make us too ill, too quickly, they don’t get much chance to spread because we either collapse into bed, away from other people, or make others leery enough of catching the disease that they take suitable precautions.

This means that from the virus’s point of view (not that it’s alive enough to have one), there is an optimum trade-off between making us sick…and making us too sick. By evolutionary standards, the common cold is a far more successful human virus than Ebola.

It also means that as viruses mutate, there is an evolutionary pressure toward that not-too-virulent optimum. The original, too-virulent, strains get out-competed by less-virulent ones we don’t take as seriously.

Not that it’s always that simple. In researching this, I came across a fascinating 2013 paper in PLOS Biology in which a team from Virginia Tech, Cornell, Princeton, and North Carolina State studied house finch eye disease, which gives the birds a nasty case of conjunctivitis (pink eye). And, while it’s a bacterial disease not a virus, the evolutionary principles are similar.

The illness first appeared in Washington, D.C., in the 1990s, but eventually spread as far as California…and was of enough concern to ornithologists that they saved strains of it from sick birds found at a number of locations on different dates.

Using these, the researchers infected birds in the laboratory to see just how bad a case of pink eye they got from each strain, and how long it took them to recover. (The disease does not kill the birds, even in its more virulent forms, though it does weaken them enough to make them enough more susceptible to predators that their numbers have substantially dwindled.)

What the researchers found was surprising. Over time, in each region, the bacteria evolved to become more virulent, not less.

But when the virus moved from D.C. to California, the strain that first arrived was relatively low in virulence. Once established in California, however, it too evolved toward greater virulence.

The researchers’ conclusion was that for the strain to get across the country, it had to not make birds so sick that they couldn’t fly that far.

“That will select for strains that make the birds less sick,” lead author Dana Hawley of Virginia Tech said in a press release. “But when it gets established in a new location, there are lots of other potential hosts, especially around bird feeders. It can evolve toward being a nastier illness because it’s getting transmitted more quickly.”

What does that mean for COVID-19?

Potentially, a lot, because our efforts to control it will affect which forms of it are most likely to succeed.

If, like house finches at bird feeders, we naively gather around the water cooler, crowd into bars, or otherwise make ourselves into easy targets, it could become more virulent.

If, on the other hand, we work to maintain social distance, wear masks, and otherwise work to ensure that, like finches flying across long distances, the virus can’t do it if it makes its host too sick (in our case, sick enough to sound the alarm), we may drive its evolution toward less-virulent forms.

That may (or may not) have been what happened to the Spanish flu.

The Spanish flu hit in 3 major waves: spring 1918, fall 1918, spring 1919. The first was relatively small, compared to what would follow.

But that made people overconfident when it came back in the fall—a mistake that helped lead to America’s ultimate tally of 675,000 deaths.

When it came back yet again in the spring, public health officials had learned their lesson from the fall, and clamped down hard, after which it largely disappears from history.

One theory is that by the end of the third wave, enough people gotten it to create herd immunity. But another is that the spring 2019 clamp-down drove its evolution into less virulent forms that then disappeared from public sight.

Which of those theories is correct, I don’t know. But like the house-finch study, the history of the Spanish flu does suggest that while Trump is correct that these things can disappear without a vaccine, he is wrong to think we might achieve that simply by returning to business as usual–not, at least, without severe consequences.

Rather, we need to think like evolutionary biologists and work to drive the virus in a direction we can more easily live with until we get a vaccine.

And that means being very cautious about exactly what we do, as we reopen the economy.