Pathogen emergence and transmission are guaranteed.

Diseases have been called “our deadliest enemy,” often posing a greater danger than combat. A century ago, the 1918 influenza pandemic infected one-third of the world’s population, killing one in fifty people.7 Twice as many people died from that pandemic as were slaughtered in combat in World War I. Over the full twentieth century, infectious diseases—what some scientists dubbed the “oldie moldies”—killed twenty times as many US citizens as wars.8

Yet the twentieth century also marked a turning point in the war against disease. In 1900, infectious diseases were the leading killers in the United States, with pneumonia, influenza, tuberculosis, and gastrointestinal infections ranking as the top causes of death.9 By the start of the twenty-first century, following a hundred years of advances in vaccines, antibiotics, and sanitation, infectious diseases were not among the top five causes of death in the United States. Only in the poorest nations were people more likely to die from infectious disease than anything else. From 1970 to 2016, worldwide mortality from infectious diseases dropped from fifteen million (35 percent of all deaths) to eight million (15 percent of all deaths).10 Consequently, people began to think of public health less as a matter of collective action, and more as a function of personal decisions such as diet and exercise.

Then, at the end of 2019, a new infectious disease threw the world into chaos. COVID-19 is a coronavirus—a specific kind of RNA virus that has proven especially virulent. SARS and MERS are forms of coronaviruses. Many coronaviruses are mild. When you catch a cold, there’s about a one in six chance it’s a coronavirus (the rest of our colds are rhinoviruses, which are also RNA viruses, but lacking some of the features of coronaviruses such as a viral envelope). Designing a vaccine against a coronavirus is tricky. Coronaviruses infect the upper respiratory tract, an area that we think of as being inside our body, but that our immune system regards as almost external. As one expert remarked, “It’s a bit like trying to get a vaccine to kill a virus on the surface of your skin.”11

COVID-19 is also highly infectious. Doctors measure disease transmission by calculating the reproduction ratio, or R0. This measures how many people each patient can be expected to infect. If the R0 is above one, then the disease will spread. If it is below one, the disease will die out because it cannot infect enough people. Seasonal flu has an R0 of one to two, meaning that each person who gets it infects one or two others. Common colds have an R0 of two to three. Smallpox has an R0 of five to seven.12 Without physical distancing, COVID-19 has an R0 of between two and six, meaning that each person can be expected to infect two to six others.13 Some who contract COVID-19, especially younger patients, may be infectious despite having no symptoms. In February 2020, COVID-19 was spreading so rapidly through Italy that the number of cases was doubling daily. Vaccines, mask-wearing, social distancing, and enforced lockdown measures help slow the spread, but more infectious virus strains (such as variant B.1.1.7) have a higher R0, making them harder to control.

In 2020, COVID-19 claimed 1.8 million lives, and the death toll in 2021 is likely to be higher still. These huge numbers are of a similar magnitude to tuberculosis, which kills 1.3 million people annually. The economic cost of avoiding the virus has been massive. Globally, hundreds of millions of people have lost their jobs, and as much as $9 trillion of economic activity may be destroyed.14 For the first time in the twenty-first century, world poverty rates are expected to rise.15 The Great Lockdown led to the worst economic slump since the Great Depression.

COVID-19 has also been a reminder of how modern living has affected the ability of viruses to jump the species barrier. The spread of human settlements and livestock farms next to natural forests raise the odds of animal viruses infecting humans.16 Three-quarters of new human diseases—including HIV/AIDS and Ebola—have their source in other animals.17 Each year, five new diseases emerge.18 When researchers took blood samples from bats in twenty countries, they estimated that there are over three thousand potential coronaviruses, most of which are yet to be described.19 Transmission to humans is commonplace. Every year, more than a million people are infected by bat coronaviruses.20

With their mind-boggling numbers and ability to replicate speedily, viruses mutate more rapidly than any other organism.21 Over the past eight million years, humans have evolved by 1 percent.22 Many viruses can evolve by more than this in just a few days. As COVID-19 has shown, the factors that have driven prosperity—urbanization, busy workplaces, and global travel—also allow viruses and bacteria to spread further and faster than they could in the era of the black death.

The coronavirus pandemic has prompted an unprecedented surge of research into how the virus emerged, and how to treat it. “Wet markets”—wild animal markets, in which dozens of different species are caged close together and sold for human consumption—have been described as “the perfect place” for viruses or bacteria to jump the species barrier.23 As Laurence Fishburne’s character says in the film Contagion, “Someone doesn’t have to weaponize the bird flu—the birds are already doing that.” China’s wet markets were partially shut down after the 2003 SARS, 2013–2014 bird flu, and 2019–2020 coronavirus outbreaks. Many have pushed for a permanent end to the trade, though experts note that a full ban would also require a strategy for curtailing the unregulated black market that would inevitably emerge in response.24

Put enough monkeys in a room with enough typewriters, and it’s a sure bet that one monkey will eventually murder another with a typewriter. Likewise, the mathematics of viral replication is guaranteed to keep creating new diseases. As molecular biologist Joshua Lederberg ruefully observed of new infectious diseases, “It’s our wits versus their genes.”25 Viruses are not alive; they are virtual organisms, running on the hardware of plants or animals, and reproducing by infecting cells. Viruses outnumber all living things by a factor of ten. A gallon of seawater or pound of dried soil contains around four hundred billion virus particles.26 So pure chance will invariably lead to new diseases, and close-knit societies risk spreading them quicker than ever.

But bad luck isn’t all we have to worry about. Bad actors are looking to create and weaponize biological agents too. Biological warfare dates back more than two thousand years.27 In the Trojan War, archers dipped their arrows into poison. Roman commanders poisoned the wells of besieged towns. Mongol attackers catapulted the bodies of plague victims over castle walls. In the Ohio River valley, British soldiers gave smallpox-infected blankets to Native Americans. During World War I, Germany attempted to infect Allied horses with anthrax.

In World War II, advances in microbiology led the Soviet Union, Germany, Britain, and the United States to develop bioweapons programs. Japan created plague epidemics by dropping infected fleas from aircraft into Chinese cities. During the 1950s and 1960s, the United States carried out an active bioweapons program, investigating yellow fever, typhus, and the plague.28 The program also experimented with how to disperse the germs, using pseudo biological weapons. In 1965, government agents at what is now Reagan National Airport secretly sprayed harmless bacteria onto passengers. In New York the following year, agents smashed bacteria-filled light bulbs in the subway. The government sprayed chemicals from aircraft onto north central Texas and from ships into the San Francisco Bay. By the time it was shut down in 1969, the program had mass-produced a half-dozen biological weapons, including anthrax, tularemia, and botulism. These weapons were destroyed over the next few years, as the United States signed onto the Biological Weapons Convention, banning all biological weapons.

The Soviet Union signed the Biological Weapons Convention as well, but continued to secretly develop biological weapons through the 1970s and 1980s. Employing thirty thousand people across eighteen laboratories and production centers, the Soviet Biopreparat program created “veepox,” a hybrid of Venezuelan equine encephalitis with smallpox, and “ebolapox,” a hybrid of Ebola with smallpox.29 It stockpiled twenty tons of smallpox, twenty tons of bubonic plague, and hundreds of tons of anthrax.30 Only when leading scientists defected and exposed the program did the Russian leadership admit its existence and begin closing it down.

The Soviets weren’t the only ones skirting the law. During the 1980s, Saddam Hussein produced over a hundred million gallons of biological weapons, including botulinum toxin, anthrax, and aflatoxin.31 So lax were the international controls that Hussein’s scientists were able to source much of their equipment and materials from Germany, France, and the United States. Adhering to guidelines that encouraged the free exchange of samples among researchers, the American Type Culture Collection in Virginia mailed strains of the bubonic plague, West Nile virus, and dengue fever to Basra and Baghdad, where they were used to develop Iraqi germ weapons.32 In the twenty-first century, most government-run biological weapons programs seem to have ceased, though the Syrian regime, aided by the Russian government, appears to have used chemical weapons (chlorine and sarin) to attack dissidents.33

Beyond governments, terrorist groups have recruited scientists to work on germ warfare. In 1984, the worst biological terror attack in US history took place in the Dalles, a farming town of about 10,000 people situated an hour and a half’s drive west of Portland, Oregon. Thousands of members of a religious cult run by Bhagwan Shree Rajneesh had established a commune and won political control of the nearest town, Antelope (which they renamed “Rajneesh”). They planned to win county elections in Wasco County by deterring other residents from voting. To achieve their goal, they sprinkled salmonella into the salad bars of ten restaurants, poisoning 751 people, all of whom eventually recovered. The decision to use a nonlethal bacteria came only after cult members had considered deadlier alternatives. As part of their planning, they obtained samples that would have caused typhoid fever, tularemia, and shigellosis. They also tried to culture HIV/AIDS, drawing blood from a homeless man who was infected with the virus.34

Among the most advanced terrorist biological weapons program was that of the Japanese Aum Shinrikyo doomsday cult, which aimed to bring about the end of the world so its followers could attain salvation. In the early 1990s, cult members attempted to obtain Ebola virus in Zaire and carried out three unsuccessful biological attacks. Later interviews with cult members revealed how close they came to unleashing botulism and anthrax, failing in one case merely because they used a vaccine strain of anthrax rather than a lethal one.35 In 1995, cult members released sarin gas into the Tokyo subway system during rush hour, injuring six thousand people and killing fourteen.36 When officials later raided the cult’s headquarters at the foot of Mount Fuji, they found enough sarin to kill over four million people.37

The leading danger today arises from synthetic biology—techniques that blend physical and genetic engineering to create new life-forms. Many applications of the technology can have enormous benefits, such as helping create higher-yielding crops, novel health treatments, and new biofuels. But the same technology can be misused to alter existing bacteria or viruses in order to make them more dangerous. This might involve creating superbugs by adapting bacteria so that they are resistant to antibiotics, making vaccine-resistant diseases, changing bugs so that they produce harmful toxins, or combining multiple diseases into dangerous hybrids.

So far, this is merely the stuff of fiction. In Richard Preston’s 1998 thriller The Cobra Event, an attacker engineers a disease called “brainpox” from smallpox and the common cold. But fiction has a way of influencing policy making. Preston’s novel was reportedly influential on President Bill Clinton, who read it on the recommendation of genetic researcher Craig Venter and subsequently commissioned work from his national security advisers on the risks of recombinant biotechnology.38

In the two decades since, synthetic biology has advanced considerably. As Ord has underscored, the cost has also fallen dramatically. The project that led to sequencing the first human genome cost taxpayers $3.4 billion.39 Today, a range of US laboratories will speedily sequence your genome for less than $1,000. A Chinese company recently claimed that it can do the task for just $100.40 Gene editing technology has now become so simple that high schoolers are being taught to create proteins containing genes that make them resistant to antibiotics.41

Intelligence agencies are concerned. A leading review of the health security implications of gene editing pointed out that the techniques are likely to be valuable in identifying, diagnosing, and treating outbreaks of infectious diseases. Yet it also acknowledged that “CRISPR gene editors could be used bluntly as a bioweapon if a delivery mechanism could be devised.”42 Similarly, the US intelligence community’s Worldwide Threat Assessment names bioterrorism as one of the threats to national security, noting that “these technologies hold great promise for advances in precision medicine, agriculture, and manufacturing, but they also introduce risks, such as the potential for adversaries to develop novel biological warfare agents, threaten food security, and enhance or degrade human performance.”43

The practical risks of gene editing were highlighted when two researchers at the University of Alberta in Canada showed that it was possible to make horsepox, a disease cousin of smallpox, by ordering parts of DNA on the internet and reassembling them. The project cost $100,000 and took about six months. Although the researchers claimed that their work could lead to a better smallpox vaccine, critics noted that an effective vaccine already exists. The research demonstrated the tension between academics’ instinctive desire for openness and the risk that malevolent actors might misuse the findings (what security researchers call a “dual use”). When the researchers submitted their findings to the journal Science, the editors replied, “While recognizing the technical achievement, ultimately we have decided that your paper would not offer Science readers a sufficient gain of novel biological knowledge to offset the significant administrative burden the manuscript represents in terms of dual-use research of concern.” But the researchers simply sent their findings to another journal, which published the study. Some scientists were outraged, with one critic arguing, “If anyone wants to recreate another poxvirus, they now have the instructions to do that in one place.”44

When it comes to bioengineered bugs, two factors determine how dangerous they are to a population: deadliness and contagiousness. These are simple concepts, but they can be tricky to measure. Do we measure the deadliness of the bubonic plague in medieval Europe or a world with antibiotics? Do we estimate the contagiousness of COVID-19 with or without vaccines?

In figure 2.1, I rely on the work of data journalist David McCandless, who has reviewed the scientific literature to estimate the deadliness and contagiousness of more than a dozen diseases. Where possible, deadliness estimates are for a patient who is untreated, and contagiousness estimates are in the absence of a concerted community response.45

Some diseases are natural-born killers. Ebola and bird flu (H5N1) kill about half of those who contract them. Other diseases are extremely contagious, spreading like a new internet meme. Mumps has an R0 of around seven. Measles has an R0 of around nine.46 But thankfully the most dangerous diseases don’t tend be as infectious. Ebola and bird flu lack the supercontagion of mumps and measles. Conversely, over 99 percent of those infected with mumps and measles will make a full recovery. Few diseases are both extremely deadly and ultracontagious. Pathogens that kill their host quickly don’t allow much time to infect others.

Yet while germs are rarely fast spreading and fatal, such a disease is not impossible. The greatest risk to humanity comes from a bioengineered bug that would fit in the top right corner of figure 2.1. This would mean that the disease had both a high mortality rate and high R0 [reproduction ratio]. In 2011, a researcher at the Erasmus Medical Center in Rotterdam reported that he had “mutated the hell out of H5N1,” and created a virus that would attach to nose and trachea cells—a contagious bird flu.47 Another example was raised in a 2018 report from the Bipartisan Commission on Biodefense: a hypothetical scenario in which terrorists released a version of the plague that had been aerosolized and genetically engineered to make it resistant to antibiotics.48