It’s not clear just what number of people in a community would need to be infected with novel coronavirus to confer a measure of herd immunity. Because that hasn’t happened anywhere just yet. When epidemiologists provide numbers from 40% to 70% of the population possibly becoming infected if novel coronavirus goes unchecked, what they’re really saying is that those are the kind of numbers needed to significantly impact the transmissibility of the virus—that famous R0 value—to the point where an epidemic can no longer sustained itself.

R0 is often treated as a single, unchanging number. It’s not; at least not in any practical sense. Features that are not baked into a virus or bacteria can affect transmissibility. Ebola, for example, has a relatively high R0 in several African nations specifically because of the way that bodies are handled by numerous people and washed after death. Take away that contact, and the disease spreads less rapidly.

One thing that has a big impact on R0 for diseases is simply population density and the amount of social interaction. If someone doesn’t come into contact with another susceptible person during the period in which they are contagious, then they can’t make someone else sick. That’s true whether that person is being held in intentional isolation at a military base, or just happens to live in a cabin high in the Rockies.

Herd immunity comes when enough people have had the disease, and developed immunity, that it generates its own kind of isolation. An infected people may meet others, but if if those people can’t be infected in turn, they don’t sustain the epidemic. When every infected person passes the disease to less than one new person, the outbreak … breaks.

So, herd immunity is a real thing. We’re all very likely to get there, and it represents what may be the only sure end to this thing (assuming this branch of beta coronaviruses don’t become endemic and throw up new variants each year so that cold and flu season becomes cold and flu and COVID season … let’s just put off that worry for now). That’s not the problem with what the U.K. is mulling. The problem is that it’s profoundly stupid. Sorry, that’s the wrong word. Silly doesn’t have the right impact. Ludicrous sounds too funny. Bad. That’s what it is. It’s a very, very, very bad idea.

For some days now, I’ve been talking about the difference between South Korea and Italy. And since they’re a big factor in this discussion, let’s peek in on where they are now.

COVID-19: Secondary Epicenters

Two weeks ago, on the last day of February, South Korea was about where the United States is now, with 2,300 confirmed cases. Italy was well behind, with less than 900 cases. Since then, Italy has continued up the same exponential curve, doubling their numbers every two to three days. On Saturday, it topped 21,000 cases. There are now more active cases of COVID-19 in Italy than there are in China. (That’s probably true for Iran, as well, since Iran’s numbers are patently false.) On the other hand, diligent widespread testing and case management allowed South Korea to grow at a much reduced rate, and to more or less level their total number of cases around 8,000.

But a better signal of how these two nations are doing can be found by looking at the other dire statistic—the number of deaths. With less than three times as many cases, Italy has racked up 20 times the number of deaths.

Italy and South Korea on Mar 13 Total Cases Deaths CFR South Korea 8,086 72 1% Italy 21,157 1,441 7%

The reason for this is simple enough. Italy has gone past the carrying capacity of their health care system. Italy actually has more hospital beds per 1,000 people and more ICU units than does the United States—or the U.K.—but their system, like ours, is designed to be efficient; scaling available beds to fit projected needs. It didn’t take hitting 30% of their population to overwhelm that system. In fact, it didn’t even take reaching 0.1%. The result is that doctors in Italy are being forced into horrible, life or death decisions, not once or twice, but hundreds of times each day. It’s why in Italy, the obituaries are now the largest section of many papers.

South Korea didn’t just keep their numbers down through extensive testing, they also kept their deaths down by a national program of isolation and quarantine. And it didn’t hurt that South Korea has over twice the number of hospital beds per 1,000 people compared to either Italy or the United States.

What the U.K. politicians are talking about isn’t keeping a stiff upper lip, or pushing through, or toughing it out quickly. It’s killing people. Large numbers of people. Like 10 times the number of people who were killed in the London Blitz during World War II. And honestly … that’s a low number. If the U.K. needs just 40% to achieve this herd immunity, that’s 27 million cases. If the U.K. matched Italy’s case fatality rate, that would be almost 2 million dead. But it won’t be 2 million. Because in Italy, most patients are still getting hospital care. That would not be true in a U.K. overrun with millions simultaneously ill citizens. In the U.K. a critical patient, and a dead patient, would be synonymous. It’s just a blindingly awful idea. And hopefully they will realize that before this mania goes any further.

COVID-19: United States

It would be great to see evidence that the United States was on a path closer to that followed by South Korea. So far, there’s no sign that the U.S. is managing to reduce the doubling rate of the infections. But at this point, it’s genuinely difficult to see, from the numbers alone, where the nation is going.

South Korea, Italy, and United States over a 10 day period 1 2 3 4 5 6 7 8 9 10 South Korea 103 209 433 600 833 977 1,320 1,766 2,337 3,150 Italy 157 229 286 480 655 889 1,128 1,701 2,036 2,503 United States 158 319 435 541 704 994 1,322 1,716 2,269 ???

Comparing these three nations at a similar point in their outbreak shows them following remarkably similar paths. In fact, anyone tuning in on day 10 of this list might be tempted to see Italy as the nation on the path to “winning.” It was only five days later, with over 6,000 cases in South Korea, that it became clear they were turning the situation around. Italy by that point had 7,500 cases as it continued to follow the same steep course toward disaster. At midday on Saturday, the United States has already passed 2,650 cases. It seems likely the U.S. will be reporting numbers somewhere between what Italy and South Korea had on day 10 of this path. Hopefully.

The United States has not engaged the widespread, definitive testing that was used in South Korea. It is has not applied the regional lock downs around hot spots that were tried in both South Korea and Italy. But the U.S. has made moves on schools, social events, sporting events, and other activities that weren’t made in either Italy or South Korea until deeper in the outbreak. Whether that will be enough to deflect America from chasing Italy up the path to overwhelming our healthcare system … is simply not clear. We won’t have to wait weeks to find out. The U.S. is currently only ten days behind Italy.

But before anyone else suggests that the United States should just chuck it and follow the U.K. in an all-hands-on-face virus party, it might be worth checking this New York Times piece on where that could lead. Between 160 million and 214 million people in the United States could be infected over the course of the epidemic, according to one projection. That could last months or even over a year, with infections concentrated in shorter periods, staggered across time in different communities, experts said. As many as 200,000 to 1.7 million people could die. And honestly, even that is being extremely optimistic. Because those numbers are based around the kind of case fatality rate that’s being seen in South Korea. That’s a long way from the worst case.

Resources on novel coronavirus:

World Health Organization 2019 Coronavirus information site.

World Health Organization 2019 Coronavirus Dashboard.

2019-nCoV Global Cases from Johns Hopkins.

BNO News 2019 Novel Coronavirus tracking site.

Worldometer / Wuhan Coronavirus Outbreak.

CDC Coronavirus-2019 (COVID-19) information site.

European Centre for Disease Prevention and Control.

Information on preparing yourself and your family:

Some tips on preparing from Daily Kos.

NPR’s guide to preparing your home.

Ready.gov