It’s hard to predict the trajectory or the ultimate death toll of a viral bomb without knowing precisely how it was launched. As the coronavirus that was identified in Wuhan, China, in late December, continues to race around the globe, scientists are struggling to answer many vital questions: How easily does it spread from person to person? What is the real incubation period—the time during which infected people can transmit the virus before showing symptoms themselves? What is the true death rate?
Although ninety-nine per cent of the more than sixty-three thousand cases and nearly all of the roughly fourteen hundred deaths reported so far have occurred in China, that will change. It is impossible to know the number of people who left Wuhan, a city with eleven million residents, before the Chinese authorities closed it off. Nor do we know how many people boarded planes without knowing that they were carrying the virus. We will only be sure where they all went when they start to get sick. The virus is so deeply menacing that, this week, the World Health Organization carefully named it covid-19—to avoid using the names of people, geographic locations, or even animal species, which could lead to racial attacks and the needless slaughter of animals.
Despite its severity, however, there is almost nothing surprising about this pandemic. It has been utterly predictable in nearly every way: from the nature of its emergence, to its rapid international dissemination, to its clear potential to sicken people and kill them. What is surprising is the fact that we are not better prepared for this kind of assault. As the late Nobel Prize-winning molecular biologist Joshua Lederberg put it, in what is perhaps both his most famous and his most ignored warning, viruses pose “the single biggest threat to man’s continued dominance on this planet.” As the world learned in 1918, when influenza killed at least fifty million people, there is no weapon as lethal that is also as widespread.
Moreover, these viral invasions often move in obvious, specific patterns. No one who has ever glanced at a textbook on emerging infectious diseases or, for that matter, read the science section of a newspaper, could have been surprised to learn that bats were the original host of this virus, or that humans almost certainly acquired it from an intermediary species—in this case, probably pangolins, which are thought to be the most heavily trafficked animals on Earth. Pangolins are prized for the supposed medicinal properties of their scales, and they appear to have been sold at the seafood market in Wuhan where the epidemic appears to have started.
Infectious diseases that leap from animals to humans are called zoonoses. They do it all the time. Most people remember the worldwide panic caused by Severe Acute Respiratory Syndrome, or sars, which, in 2002, led to the first pandemic of the millennium—although its global death toll was seven hundred and seventy-four people, fewer than the number of people who die in an average week at the height of an annual flu season in the United States. The sars virus, which also originated in China, passed to humans through a protein—ACE-2, or angiotensinconverting enzyme—that is found on respiratory cells, which also serve as an entry point for the covid-19 virus. They are both coronaviruses—named for the halo you see around them under a microscope—are genetically similar, and were isolated in bats. The same was true for mers, or Middle East Respiratory Syndrome, a coronavirus that began in 2012 and spread through Saudi Arabia. mers was transmitted to humans via camels, but it originated in bats, as did the Ebola virus. Marburg, a deadly hemorrhagic virus that was first described in 1967, originated in Old World fruit bats.
The reason that bats play such a significant role in the transmission of these viruses is not difficult to understand. Bats make up roughly twenty per cent of all mammal species, and many of them have unusually robust immune systems that seem easily able to defend them against powerful viruses. That makes them the perfect viral host; the viruses train themselves on the bats’ immune system, and, in the process, become increasingly able to defend themselves. Yet bats are hardly the only host of viruses that infect humans. In 2004, a highly pathogenic form of avian influenza, H5N1, which occurs naturally in wild waterfowl but can spread easily to domestic poultry, leaped from chickens to humans, setting off a frightening epidemic. In 2009, the new strain of influenza was a form of H1N1, also called swine flu, because it passed to humans through pigs; they serve as a common mixing vessel for viruses, because porcine respiratory cells are similar to ours.
The chances that a spillover, as this kind of transmission is called, will occur are greater in places where there is routine contact between animals and humans, such as the live-animal markets that are common in East Asia. If an infected pig were to sneeze in a crowded open market, it could, in theory, infect a human and set off an epidemic. Sixty per cent of the world’s people live in Asia. There are a hundred and thirteen million people in Guangdong Province alone—far more than the population of any Western European country.
These viruses all pose special threats because they are new, which means that humans have no antibodies to defend against them. The 2009 H1N1 epidemic infected at least 1.4 billion people, most of them before vaccines or treatments for the virus were available. And that was in a year when, by most accounts, the W.H.O. moved as expeditiously as it ever has. That strain of influenza killed as many as two hundred thousand people in the world—but it could have been many times worse. In 1957, for example, the Asian flu pandemic killed more than a million people. In 1968, the Hong Kong flu pandemic killed between one and four million. Maybe we will also be lucky this year. (It ought to be remembered that, even now, the seasonal flu poses a much greater threat to the health of the average American.) Unless covid-19 proves to be uniquely virulent, it will likely subside within a few months, and the danger it poses will be substantially forgotten, like that of sars, mers, avian influenza, and other zoonotic diseases. But it is too soon to know for certain.
Scientists are moving with great speed to stop this pandemic. They sequenced the virus in less than two weeks—an essential step in creating diagnostics, drugs, and vaccines, and one that only a few years ago would have taken months. But, even with expedited trials and drug development, it could take a year to create a vaccine. If this virus were to swerve out of control before then, the death rate could soar. In addition to the human toll, the economic damage to China—and, eventually, to the rest of the world—would be enormous. Industrial supply chains throughout the world have already been badly disrupted. Travel to and from China has all but stopped, and xenophobic attacks against Asians are rising. Although New York City has not reported a single confirmed case of covid-19, business in Chinatown has reportedly fallen by more than fifty per cent since the epidemic began.
Not all of this has to happen; we can do a much better job of preparing for these epidemics, just as we no longer wait to have heart attacks before we use our knowledge to limit their risk. Prevention works, and it can work with viral epidemics. For now we can be much more vigilant about improving sanitary conditions and regulating livestock in the kinds of markets where outbreaks are likely to occur. Sufficient and reliable tests for people who may have been exposed must be made readily available. There are scores of similar viruses found in host reservoirs—most notably, bats. Many of those viruses have genetic similarity to this coronavirus, and also to sars and mers. The time has come to use the modern tools of molecular and synthetic biology to make drugs and vaccines to protect us from them. We can make DNA vaccines in laboratories and store them as spare parts, just as we do with parts for a phone or a laptop. Why not work on making vaccines that would protect broadly against this entire class of virus rather than waiting for each one to attack us and then try to fight back? Today, with the annual flu, we grow most of our vaccines in eggs, just as we have for decades. It’s time to move on.
At some point, not many years from now, we will have the capacity to instantly sequence viruses and to make and operate diagnostic tests anywhere, not just in a lab. Biology is becoming digital information, and it needn’t be stored only in Cambridge, or Palo Alto, or Paris. It is already possible to transmit and print a DNA sequence using the molecular equivalent of 3-D printers—a process that could enable scientists almost anywhere to construct vaccines. Making this technique readily available should be a national and, in fact, an international priority. There are other possible solutions, such as editing the genes of pigs (and bats) to repulse the viruses that can transfer to humans. This kind of ecological intervention would be scientifically difficult, and ethically questionable. But it will inevitably be discussed, so let’s do it rationally.
Even if this pandemic passes quickly, there will be another one, possibly far more catastrophic, next year, or in ten years’ time, or twenty. All we can know for sure is that if we have any hope of containing it, the time to prepare is now.