The Plague Cycle

by Charles Kenny

  But trade also allows countries to import things they simply can’t produce at home. The United States can no longer be self-sufficient, if it ever truly was. It imports the majority of the cobalt it consumes, for example.29 And even large economies can’t produce enough food in some years and need to import it: trade is a vital part of the story of the global decline of famine over the past century.

  Smaller countries often lack the market size or productive capacity to make home production of a whole range of goods feasible. Look at pharmaceuticals: in 2004, the World Health Organization estimated that twenty-seven of the world’s countries had the ability to innovate in the production of new drugs, and ten of those had a sophisticated pharmaceutical industry undertaking significant research. Thirteen more countries were manufacturing both active ingredients and finished products. That left 126 countries that either had no pharmaceutical industry at all or relied on imported ingredients for all of their production.30 Without international trade in pharmaceutical products, those countries would have no vaccines and no antibiotics. They’d suffer nineteenth-century levels of health. For all that globalization was, in the past, a force for spreading disease, today it’s simply central to planetary well-being.

  Global connections facilitated by low infection risk have sped innovation, too. Look at worldwide collaboration on the vaccine developed against Ebola in 2015: US players in the research included Yale University, the Army Medical Institute, the Walter Reed Army Institute of Research, and the National Institutes of Health. But also playing a vital role were the Institute of Virology in Marburg, Germany, as well as the German vaccine manufacturer IDT Biologika, the Canadian National Microbiology Lab, and the World Health Organization. And nine separate countries were involved in the clinical trials set up to determine if the vaccine worked.31

  Nobel Prize–winning economists Michael Kremer and Paul Romer both suggest that, over the long term, there’s a simple relationship between the size of a connected population and the speed of technological advance.32 Small, isolated communities see technological stagnation while large, integrated populations foster rapid innovation. Technological advance is the big reason global quality of life has risen so much over the past two hundred years, and the decline in infection is a big reason for the population growth and connectivity behind that advance. At a global scale, Malthus’s fear that more people would lead to greater poverty has turned out to be precisely wrong.

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  At the same time, while Malthus worried that improved health would only lead to more people living in misery, declines in infection rates have had the—mostly positive—effect of lowering birth rates.

  Luis Angeles of the University of Glasgow looked at the data on mortality and fertility around the world over the last few decades and suggests the following pattern: as child mortality declines, the number of children women give birth to declines, too—with about a decade lag. Because of the lag, and because fewer children are dying, the short-term impact of the mortality decline is a growing population. That’s why each human only shared the planet with 2.5 billion others as recently as 1950 but now has more than 7 billion potential friends and partners. Over the longer term the trend reverses: as health improves in elder children and adults as well, fertility rates drop further, and population growth begins to slow, or even reverse.33

  Take the Middle East: In 1960, about one-quarter of children in the region died before their fifth birthday and the average woman gave birth seven times. In 1980, child mortality had halved, while fertility rates remained largely unchanged. But by 2000, fertility had begun a rapid descent to three births per woman. One impact of these changes is that the chance that a woman in the Middle East will watch one of her children die before the age of five has fallen from ubiquity to rarity: about 85 percent would have lost a child in 1960, compared to 10 percent today.

  According to the United Nations, the number of children born to the average woman fell from 5.8 to 2.3 in both Latin America and Asia between the early 1950s and the first decade of the new millennium. Africa lagged, but nonetheless the birth rate there fell from 6.6 to 4.9 children over that time.34

  The decline in both fertility and young mortality has helped age populations. In 1980, the global median age was twenty-three. By 2050, it will be thirty-eight. Work by Harvard’s David Bloom suggests there can be a “demographic dividend” during these population changes.35 After birth rates fall, the proportion of the population that is of working age climbs (because there are fewer school-age children) before it eventually falls (because there are more retirees). More workers and fewer dependents in that middle period allows for higher rates of investment and growth.

  But the dividend only pays out if all of those young people have something productive to do. In East Asia in the last decades of the twentieth century, they flocked to factories and manufactured the toys, clothes, and electronics stamped Made in Thailand or Made in China that were exported to Europe and the US. Bloom suggests that productive use of the “youth bulge” may have accounted for as much as a third of East Asia’s miracle growth rates, catapulting countries like South Korea to high-income status and leaving China the largest economy in the world.

  Other regions including the Middle East haven’t done as well in converting the health revolution into an economic revolution. The few large firms there were kept in business through government contracts and favorable treatment by regulators—not by producing globally competitive products. There’s no Middle Eastern equivalent of Hyundai or Lenovo, exporting cars or computers around the world. And so there were few good jobs, but a lot of frustrated job seekers. They had nowhere to go but the street. The lesson for Africa—still undergoing the transition to low birth rates—may be that a well-managed demographic dividend leads to East Asian growth rates, while a poorly managed age transition leads to the Arab Spring and (potentially) its grim aftermath.

  As well as producing a bulge in the working-age population, changing demographics mean that women can spend more time in the workplace. In the US, an average woman born in 1900 would be pregnant for more than a third of the time between the ages of twenty-three and thirty-three, and nursing for about a third more. Her compound risk of dying from complications of pregnancy or childbirth was about 3 percent, and more than half of all women suffered some sort of pregnancy- or childbirth-related disablement. Thankfully, risks of serious disablement from a pregnancy are a fraction of that level today—and women are getting pregnant less often. Not surprisingly, that’s had a dramatic effect on their ability to work outside the home. Only about 3 percent of married women were in the US workforce in 1890. By 1990, the figure had reached 70 percent.36 The decline of disease has started to reverse the millennia-long “civilized” subjugation of women.

  Not just women benefited from somewhat increased liberty as infection rates fell. Infectious disease risk has long been among the most common reasons—or, at least, excuses—to regulate the behavior of both sexes. Across the world, countries where pathogens are more prevalent have a greater tendency to regulate or stigmatize promiscuous behavior.37 But as infection risk declined, so did the perceived need for some of these strictures. The sexual revolution of the 1950s and ’60s followed a period in which infectious diseases—including a number of sexually transmitted diseases like syphilis—had been in retreat for two generations thanks to antibiotics, and against the backdrop of a declining birth rate. Result: a new view that sex could be for fun and bonding rather than just procreation—homosexual and masturbatory sex included. Indeed, the number of countries worldwide where homosexuality is illegal has dropped from 150 in 1960 to 72 in 2017.38

  Improved health alongside declining fertility has also been a factor behind increased investment in education. Economists Daniel Cohen and Laura Leker suggest that, across countries over the past few decades, adding one year to life expectancy at birth leads parents to send their kids to school for an extra three months.39 One reason for the link: it makes more sense to i
nvest in a child’s education if the child is likely to live long enough to use what they learn.

  Sadly, the AIDS epidemic has given us the ability to watch the health-to-education link operate in reverse. Economist Sebnem Kalemli-Ozcan looked at demographic trends in a number of African countries and argues that AIDS has encouraged parents to have more children—to ensure some survive. That forces lower investment in each individual child’s education.40 Between 1985 and 2000, high HIV/AIDS prevalence in countries like the Congo led to the average woman having two more children, and the average child receiving more than a third less schooling, than in African countries that had comparatively low HIV prevalence.

  Better health prospects in general can also affect our response to new disease threats. University of Chicago economist Emily Oster demonstrated this looking at how HIV affected sexual behavior among African heterosexual men and US homosexual men. While both groups were at comparatively high risk of the disease, only the US homosexual men altered their behavior in response to risk—reducing the number of partners they had sex with by 30 percent between 1984 and 1988 alone.

  Oster suggests the reason is that African men had lower life expectancy, AIDS or no—so they had a lower return to protecting themselves from HIV. She found that richer African men with a higher life expectancy absent the AIDS threat were more likely to reduce their number of sexual partners—their payoff to monogamy was higher. If African men had the pre-HIV life expectancy and wealth of American homosexual men, she suggests, their behavior change would have been as dramatic. Poor health prospects encourage risky health behavior, Oster concludes.41

  If you’re probably going to die from an infection tomorrow, your attitude toward risking your life today in a fight might be more relaxed as well. That suggests that improved health and reduced pathogen stress might also be a factor, among many, in lowering rates of violence in a post-Malthusian world. Global battle deaths in the new millennium are at one-tenth their level in the 1950s.42

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  The overall link from health to wealth and broader well-being isn’t simple, immediate, and certain. Considerably improved health, even in some of the world’s most benighted spots, hasn’t made South Koreas or Singapores out of Niger or the Central African Republic.

  What bedevils some countries’ development prospects remains stubbornly intractable. For example, there’s an active debate among developmental economists as to why tropical regions with their high burden of infectious disease are still poorer to this day. On one side are those who think that the current-day impact of disease is reason enough to expect greater poverty. Scourges such as malaria, diarrhea, AIDS, and dengue impact the ability to work, learn, invest, and so on. Jeffrey Sachs at Columbia University and former US treasury secretary Lawrence Summers at Harvard are two economists who have emphasized the contemporaneous impact of infection on economies.43

  On the other side are economists, such as Daron Acemoglu and James Robinson, who emphasize the role of history—the impact of disease on the shape of colonial institutions, and through that on the shape of modern political and economic systems.44

  Both sides have it right. There’s evidence for historical and contemporaneous impacts of disease on economic success. Tropical disease has delivered a double burden: a grim history of unequal institutions and a grim present of sickness and death. In connection with that, Harvard’s Philippe Aghion points out the obvious: countries that start healthy and grow healthier over time experience far more rapid economic growth than countries that start and stay unhealthy.45

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  Nonetheless, globally, victories over infection have dramatically reduced barriers to connection, increased the number of people to connect with, and ensured that the newly connected have the skills and outlook to make the most of the opportunity. All of that helps to explain why a planet that in Malthus’s day was home to a billion people living, for the most part, at subsistence level, is, two centuries later, home to more than 7 billion people with average incomes more than twelve times higher.46

  Although the final data for 2020 will almost certainly show an increase in global poverty as a result of the Covid-19 depression, the decline in the number of extremely poor people living on less than $1.90 a day—from about 60 percent of the world’s population in 1970 to less than 10 percent in 2017—is a sign of the ongoing global transition toward a healthier, wealthier, and happier planet. The rollback of infection hasn’t only erased the losses that the average human suffered when civilization spread, it has helped vault mankind to an unprecedented standard of living.

  That transition has reshaped the global economic order. For most of the last two thousand years, the world’s two most populous countries, India and China, have vied for the top economic spot. The health and economic divergence that began with the Industrial Revolution left China and India behind, overtaken by Western Europe, Japan, and the US. But with the progress of the last couple of decades there has been dramatic convergence. In 1950, China’s economy was a little more than two-thirds the size of the United Kingdom’s, and less than one-fifth the size of the US economy.47 At some point toward the end of 2014, China’s output overtook that of the United States and the country became the largest economy in the world.

  Just as, over the last five hundred years, the distribution of global infection helped determine which countries were colonized and by whom, in the last fifty years the fight against infection has, once again, transformed the contours of world power.

  To be sure, resurgent infection can still do immense harm. That’s the risk the world will always confront, most recently illustrated by Covid-19. The risk has three parts: urbanization and globalization are still powerful forces for disease development and spread, our old instincts regarding exclusionary response are only just under the surface, and we’re misusing our tools to keep infection at bay. In 2020, we saw all three problems play a role with the spread of the coronavirus and our response to it.

  CHAPTER NINE The Revenge of Infection?

  We are now in the throes of a third epidemiological transition, in which a resurgence of familiar infections is accompanied by an array of novel diseases, all of which have the potential to spread rapidly due to globalization.

  —Kristin Harper and George Armelagos

  World airline routes. Every (normal) year 1.2 billion people travel to another country as a tourist. (Credit: Mario Freese)

  At the turn of the new millennium, London’s population, a shade over 7 million strong, was 27 percent foreign-born, with eighteen different source countries contributing more than thirty thousand residents. Meanwhile, New York’s 8 million residents included 33 percent foreign-born, with more than thirty source countries contributing more than fifteen thousand each.1 Not surprisingly, both are travel hubs: London’s Heathrow, Stansted, and Gatwick airports regularly serve a combined 144 million passengers a year, while New York’s JFK, LaGuardia, and Newark serve 132 million.

  The global metropolises of London and New York have been home to some of the highest average life expectancies and richest people ever. But they were both hit early and tragically hard by Covid-19. They demonstrate both the benefits of a world made safe for connected cities and the costs if we don’t keep up our guard against continued disease threats.

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  In 1855, the missionary Samuel Livingstone came upon Victoria Falls. That discovery marked the end of the great age of land exploration. A century later, humanity regularly traversed every region of the world. It seemed reasonable to assume that the risk of encountering a completely new disease—rather than spreading an old one—would have declined as a result. And in 1962, Nobel Prize–winning virologist Sir Frank Burnet suggested that writing about infectious diseases “is almost to write of something that has passed into history.… The most likely forecast about the future of infectious disease is that it will be very dull.”2

  We know it hasn’t turned out that way. In fact, even as Burnet was writing, a disease was alrea
dy circulating in the Congo basin that would shatter predictions of an uneventful infectious future—and within a few years it would spread to the US. On June 5, 1981, the Centers for Disease Control and Prevention in Atlanta issued a new Morbidity and Mortality Weekly Report. The subject was pneumocystis pneumonia, a disease “almost exclusively limited to severely immunosuppressed patients” that had infected five young gay men in the period between October 1980 and May 1981. The cases indicated the possibility of “an association between some aspect of a homosexual lifestyle or disease acquired through sexual contact” and “the possibility of a cellular-immune dysfunction.”3

  These sufferers were getting sick from conditions that implied their immune system—including the white blood cells that are meant to attack invading bacteria and viruses—was deficient. People with healthy immune responses simply didn’t get the type of pneumonia these patients had. And whatever had happened to their immune system wasn’t a genetic problem, it had been acquired—previously, the victims had been perfectly healthy. By September 1982, when 593 cases of the condition had been reported to the CDC, the disease had an official name: Acquired Immune Deficiency Syndrome.

  The human immunodeficiency virus (HIV) was the cause of AIDS. HIV emerged as a mutation from a simian version as long ago as the 1920s, probably in Kinshasa in the Democratic Republic of the Congo. But the first epidemic only occurred fifty years later in Kinshasa, perhaps sadly and ironically helped in its spread by the reuse of needles in immunization campaigns (the virus may have come along for the ride between injections).4