In This Issue
Winter Issue of The Bridge on Complex Unifiable Systems
December 15, 2020 Volume 50 Issue 4
The articles in this issue are a first step toward exploring the notion of unifiability, not merely as an engineering ethos but also as a broader cultural responsibility.

A Global Pandemic as a Complex, Unifiable System

Thursday, December 17, 2020

Author: Harvey V. Fineberg

Global pandemics result from an emerging infection that causes notable disease in many countries in different parts of the world. At the margins—exactly how many countries and continents and with what degree of disease severity—public health authorities may dicker over the definition or its applicability to a situation. But when beset by a raging outbreak such as covid-19 that can cause more than a million deaths around the world—in every global region, in countries large and small, rich and poor—we can confidently declare a global pandemic.

A global pandemic is by nature a complex system both in its cause and in its expression. This means that the triggers and the consequences of a pandemic each have components with deep interdependencies: couplings that are loose or tight, direct or indirect; causations that are alternately necessary, joint, conditional, and relative; feedback loops that are amplifying or dampening; and indeterminacies that are partly stochastic features of the natural world and partly an expression of the limits of understanding. In sum, everything that makes a system “complex.”


In terms of causation of an emerging infection, it is often convenient to identify system components, attributes, and relations at four levels: the infectious organism in question; human and social activity and behavior; animal populations[1]; and the environment and ecosystems in which the organism, animals, and humans interact. These are the building blocks of the systems approaches in the interdisciplinary fields of One Health and Planetary Health.

Most emerging infections, including those that produce a global pandemic, begin as a zoonotic transmission, that is, from an animal reservoir to a human. Many of these zoonotic infections are limited because the organism that infects the human has not adapted to spread readily from one person to another. However, in instances where the organism does spread easily from one human to another—such as with SARS-CoV-2 (the organism that causes the disease covid-19)—an outbreak or pandemic may ensue.

This understanding of causation puts a special premium on the interactions among humans, animals, and infectious organisms—in systems terms, on the -dynamics of the relations among the components. Human populations have grown in number, intensified the density of urban environments, and spread to live in more rural areas (case in point: Lyme disease and proximity to deer, mice, and ticks). Worldwide, domesticated animal populations have grown an order of magnitude faster than the human population. And wet markets popular in various parts of the world bring humans and live animals regularly into proximity with one another; civets, a delicacy in China, are believed linked to the origin of the first SARS outbreak in 2002.

Various organisms have different propensities to cross species. Influenza is notorious for its ability to reside and genetically recombine in a variety of avian and mammalian species, including humans.

Prepandemic global travel conveyed millions of individuals, including any who may be infected, within a day’s time to any other spot on the planet. A systems understanding of emerging and pandemic infection thus requires a unifying portrait of a complex set of components and interactions.


The expression of a pandemic is similarly complex and occurs at multiple levels:

  • as disease in an individual;
  • as a public health problem of community transmission, morbidity, and mortality;
  • as a medical system challenge to care for the sick and protect the health of caregivers;
  • as an economic crisis that puts millions out of work and undermines economic activity;
  • as a social crisis that throws into question the role of science, confidence in political and health leaders, and the role of international cooperation and agencies such as the World Health Organization.

Each outbreak or pandemic has distinctive clinical and public health features, even among related organisms, such as different strains of influenza or different coronaviruses. For example, in 2002 the first SARS outbreak spread to about 8000 persons, with a mortality rate of about 10 percent. The SARS-CoV-2 virus spreads more readily but produces a wider spectrum of illness (including up to half who will remain asymptomatic) and lower mortality rate among cases. However, since so many millions more are infected by SARS-CoV-2 compared to the original SARS virus, the number of fatalities is more than a hundred times greater, even as the mortality rate among cases remains lower.

Each component of the pandemic’s expression—as an individual health problem, as a public health problem, as a healthcare challenge, and as economic and social crises—contains subsystems that adumbrate the scope of the challenge. For example, as an individual health problem and medical care challenge, key sub-systems include the development, evaluation, and deployment of diagnostics, treatments, vaccines, and other modalities of intervention; adequacy of hospital and intensive care beds, ventilators, and personal protective equipment; numbers of trained health personnel; and smoothing strategies to spread the load of patients with covid-19 and to care for others in need of medical treatment.

For the vaccine component of a solution, as another example, subsystems include public and private research, product development, testing for safety and efficacy, evaluation of performance and risk, regulatory standards and approval mechanisms, manufacturing and distribution (locally, nationally, globally), priorities for use, and, very importantly, capacity to administer the vaccine to large numbers of people in a condensed time period.

Unification for Effective Intervention

Coping with such complex systems and subsystems in a global pandemic introduces the question of unifiability across systems. In fact, unification across systems is essential to successful intervention. The requirements for preparation, prediction, assessment, response, and adaptation in relation to global pandemics all depend on a unified approach, one that simultaneously takes account of actions and relations among system and subsystem components.

Systems models, at different levels of abstractions with some more precise than others, are one way to articulate the unity of a complex system such as global pandemics. In general, the models may be descriptive (allowing focus on one part of the system without -losing sight of the whole), predictive (allowing manipulation of one or another set of variables to determine effect on results), or decision support (laying out scenarios, probabilistic events, and possible outcomes). Any -model is necessarily a simplification of the actual situation, and its utility depends on the completeness of inclusion of relevant attributes, accuracy of understanding of dynamic dependencies, and ability to estimate attendant uncertainties.

Beyond modeling, the unifiability of a global pandemic as a whole system finds its expression in leadership (that begins with a unified command structure), strategic emphasis (that takes account of priorities and interdependencies across subsystems), and communication (that consistently conveys a coherent sense of what steps will be taken, what will be accomplished by when, and what needs to be learned).

In a complex and overwhelming systems challenge, such as a global pandemic, the ability to unify understanding and response through leadership, strategy, and communication may make all the difference to success or failure and to lives lost or saved.


[1]  When a disease may be spread by an insect vector, special attention to that component of the ecosystem is warranted.

About the Author:Harvey Fineberg (NAM) is president of the Gordon and Betty Moore Foundation, and former president of the Institute of Medicine (now National Academy of Medicine) and provost of Harvard University.