It has been so long since a disastrous contagion swept through the Western world that most of us have forgotten how deadly contagious diseases are. The scariest in my lifetime was polio, because the disease could cripple as well as kill. I remember lining up at the local high school with all the other kids to get the first polio vaccine.

In 1969, the Hong Kong flu swept through my college, leaving me and many others—all healthy young people—bedridden for more than a week. The Spanish flu in 1918 killed between 25 and 50 million people—more than all the deaths caused by the violence of World War I.

Historically, things were worse. Yellow fever took nearly half of all the British who went to the West Indies. The disease killed Tom Fowle, the fiancé of Jane Austen’s sister Cassandra, on a military ship cruising in the Indies. So many white men died in the region of "yellow jack" that the British military purchased 13,400 enslaved blacks to fill out their ranks. The men were promised freedom at the end of their service.

Jane and Cassandra nearly died from typhus as children. The mother of their cousin did die from it when she came to care for the two girls and her own daughter, who was also infected. Jane also contracted whooping cough (pertussis), and probably other diseases. None of Austen's novels deal with a major epidemic, though they would have broken out regularly. Emma (above, by headline), would have been in particular danger because of her regular visits to villagers suffering "sickness and poverty together."

People should be aware that Native Americans were largely wiped out by pestilence brought to the New World by Europeans. The only reason the New World could be settled en masse is that upwards of ninety percent of its original inhabitants had died since the first Spanish explorations. Smallpox was one of the most devastating. Native Americans had no resistance. Smallpox might kill 30 percent of an English village. It could wipe out most of a North American village.

Smallpox vaccinations began to occur after Edward Jenner’s proof that the method worked. Mrs. Lefroy, one of Austen’s mentors, led a campaign to vaccinate children in Hampshire in the late 1790s. The practice remained controversial, though. Jane’s brother Edward did not have his family vaccinated until 1810.

Some diseases no longer frighten us because vaccines have largely eliminated them. During Jane Austen’s day, measles killed as many people as smallpox or typhus, or it weakened individuals enough that they succumbed to others. In the early 1500s, measles in Cuba killed two-thirds of the people who had survived smallpox and killed half the people in Honduras.

Despite the development of modern vaccines, the high contagion rate by measles makes it a continued scourge. Measles, which is twice as infectious as the flu and covid-19, caused 134,200 deaths in 2015, according to the World Health Organization.

In avoiding vaccines, people have counted on “herd immunity” protecting them—because the rest of us were vaccinated, the risk of measles spreading was almost nil. Now, however, so many people have used the same ploy that gaps have opened in herd immunity. Refusal to vaccinate has led to a return of the disease in the U.S.; deaths rose from 37 people in 2004 to 667 people in 2014, the last year for which reliable numbers are available. Seven children died of pertussis in 2016, despite the availability of a vaccine.

Children under the age of five have always been the most likely to become infected and to die from measles and pertussis. Older people are more likely to die of the flu and related infections. People beyond the age of sixty have weaker immune systems and are more likely to have developed other conditions that render them more susceptible.

This recapitulation brings us to the current covid-19 pandemic. Health authorities have urged serious action, including shutting down all but the most critical activities and self-isolating to avoid the spread. Some people are claiming that these actions are too extreme. If the pandemic peters out, no doubt a few naysayers will claim the whole thing was an overreaction.

Truth is, if we do all the right things, the naysayers will be right: the pandemic will fade away. They’ll be wrong, however, about the reason. It’s not that fears of the disease were overblown. It’s that we took the steps to break the power of doubling.

Contagions spread in predictable ways. Worldwide, covid-19 cases are doubling every five days as one person infects several more. In Italy, cases are doubling every three days, which is why they have been overwhelmed. That's why we've seen diseases in the past that have killed large parts of the population.

But if you have only 20 or 30 cases, you figure the crisis will be far down the road. That's what the naysayers assume. They don't recognize the danger of doubling. If you put one grain of sand in the first square of a chessboard, and double it to two in the next square, and double that to four in the next, and so on across the board … by the time you’ve gotten to the last square, you’ll have more grains of sand than exist on the earth!

If the U.S. has 4,000 cases today, and the cases double every five days through a normal spread through the population without any preventive measures, we’ll have 32,000 cases by the end of the month, 256,000 on April 15, a million cases by April 25, and 16 million cases by May 15. (The official U.S. number jumped from 3,400 to 5,200 overnight. I'm using 4,000 as a convenient base.)

At 16 million cases, one to two million people will require hospitalization. That number overwhelms our hospital beds, ventilators, and other infrastructure. Ventilators are the critical device for compromised lungs. The load also overwhelms doctors, nurses, and other care providers. (See Italy.)

Very likely, the current number of U.S. cases is much higher. One county in California just had its first two deaths. With a mortality rate of 2-3 percent, this means about 100 people are infected. Yet the official county number is only 20. If this is typical countrywide, then the current U.S. number is closer to 20,000 than 4,000-5,000. This means 80 people could be wandering around in that one county, unknowingly infecting others, while 15,000 people might be doing the same nationwide.

We don't have good numbers because, for inexplicable reasons, the government did not authorize private labs to create testing kits all the way back in January. We’re only just now getting a fair number in the field to know what the correct caseload might be. We could be hitting the “knee of the curve,” when the numbers shoot up into the millions, even sooner than mid-May.

The pandemic affects more than people with the disease. People needing treatment for other serious diseases, including the flu, may have no care available. If you need emergency surgery, an acquaintance pointed out, your doctor likely will have been working round the clock for weeks. Your surgical station might be a tent on the front lawn. The hospital might be low on antibiotics or other meds. And, of course, you’ll be surrounded by people carrying a deadly disease.

There’s only one way to break the power of doubling: end the physical connections between people that enable the disease to spread. Doubling once every five days results in a number 64 times as large as doubling once a month. By separating ourselves, we can flatten the curve, spread out and reduce the number of cases, keep the peak below the level of “hospital collapse,” benefit from a possible  summer falloff, and hang on until a vaccine arrives in 12 to 18 months.

If we do bring the pandemic to a halt, let’s be wise enough to know why it stopped. Not because fears were overblown but because we acted aggressively when the numbers were still low. Now is when we can make a difference. Let’s do the right thing—which is to remain as far as we can from as many people as we can until we have a handle on this thing.

Anyone for reading a great Austen novel in isolation under a tree?

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The Marriage of Miss Jane Austen, which traces love from a charming courtship through the richness and complexity of marriage and concludes with a test of the heroine’s courage and moral convictions, is now complete and available from Amazon and Jane Austen Books.