Modeling Pandemics, or, How Mathematics Changes the World Nathaniel Hupert (bio) it is a truism that mathematics laid the foundation for key advances in human achievement—agriculture, commerce, exploration, splitting the atom, the Internet—but rarely has there been a time when so few mathematical equations have so greatly changed the course of global events as in the winter of 2020.1 Pandemic models of the SARSCoV-2 virus, the cause of the infelicitously named COVID-19 disease that has gripped the world this year, have led to lockdowns of one sort or another in most countries of the world regardless of economic status or location. Some nations' responses come directly from central casting, so to speak: Germany with its comprehensive testing and top-notch clinical care; Taiwan with its remarkably efficient case finding and isolation. Others, however, have gone distinctly against type: Sweden with its seemingly (but not actually) laissez-faire approach; the United States playing perpetual catch-up after a series of out-of-character lapses from the vaunted Centers for Disease Control and Preventioncompounded by an ongoing crisis of leadership. Yet the constant across these and other nations' mobilizations is reliance on the work of a small band of mathematicians, physicists, and statisticians—mostly situated in London, Boston, Hong Kong, and Seattle; and largely using similar theoretical constructs based on the SEIR (susceptible, exposed, infectious, recovered) dynamic infectious disease model, which originated in the early twentieth century—who [End Page 253] within weeks of the first illnesses projected a combination of high case fatality and rapid propagation that quickly pushed aside any of the standard methods of policy deliberation: weighing costs and benefits, segmentation of interventions by risk group, and so on. The prospect of a 1918-like global death wave, reified by numbers and graphics and interactive websites, and quickly validated by peer review and university-backed press releases, was compelling enough that the global economy was reduced to a subset of "essential" local economies. One need only look up in spring 2020 to see what mathematics has wrought—clear skies without contrails, thanks to the more than 90 percent reduction in global air travel. How different from the early 1980s, when the human immunodeficiency virus (HIV) was for years ignored in plain sight, its lethal path traced mainly through already marginalized groups that had to fight for recognition and reaction from political and health authorities, as so eloquently described in many of the articles reprinted here. Yet here, too, there are emerging similarities between the AIDS and COVID crises, since all health catastrophes eventually compound the misery of the most vulnerable in society. Already in a number of high-income countries, the COVID pandemic has settled heavily on those who are least able to escape its path—individuals who due either to debility or destitution have to live or work in facilities where assurance of their health and safety lies in the hands of others. In the United States, for example, longterm care facilities now account for over half of the deaths from SARS-CoV-2 in many states, while prisons and slaughterhouses have been the sites of its most intense outbreaks. But worse is to come: the magnitude of the economic shock will, of course, be transmitted not to those holding the reins of the economy but to those already under its thumb. Virtually none of the models predicting COVID deaths factored in the long-term health and well-being of individuals whose lives are being transformed by the lockdowns and the consequent loss of livelihood. Paradoxically, the global reaction to a clinical disease whose age-predilection is clearly [End Page 254] skewed to the oldest among us may have its most widespread and durable impact on the youngest, factoring in the health and economic opportunity costs of the "lost spring" of 2020. Given our ongoing destruction of the natural world (a rampage that this global pause may give us a remarkable and unexpected opportunity to gauge), pandemics like COVID are likely to be more of a constant than an exception as we fully inhabit the Anthropocene. It is perhaps too low a bar to ask that, if anything valuable is to be learned...