In this report, the authors offer initial frameworks for thinking about how the United States could achieve resilience against three biological threat scenarios: a rapidly spreading transmissible pathogen, a silent pathogen infecting the population before it becomes aware of it, and a saturating scenario with a pathogen that persists in the environment. They recommend actions that governments and civil society can take to work toward resilience.

Physical Approaches to Civilian Biodefense

Identifying Potential Preparedness Measures for Challenging Biological Threats

Aman J. Patel, Thomas Milton, Andrew Graham, Samuel Reynolds, Ulrik Horn, John P. Tarangelo, Saskia Popescu, Greg McKelvey, Jr.

ResearchPublished Sep 18, 2025

Although progress in biological sciences and technologies will offer more opportunities to improve human well-being in the coming decades, this progress may also lower barriers that are blocking bad actors from engineering pathogens to cause destruction. In severe cases, the harms of future biological attacks may approach the magnitudes of the worst plagues of history—from the devastation wrought by the Black Death to the epidemics that decimated Mesoamerican societies after initial European contact.

In this report, the authors offer initial frameworks for thinking about how the United States could achieve resilience against three biological threat scenarios: (1) a fast scenario, challenging countermeasures with a rapidly spreading outbreak of a lethal human-to-human-transmissible pathogen; (2) a silent scenario, challenging detection with a pathogen that infects much of the population before infected people display visible symptoms; and (3) a saturating scenario, challenging countermeasures involving a pathogen that replicates and persists in the environment.

The authors recommend actions that governments and civil society can take to work toward resilience, including more in-depth research to better understand these scenarios and possible defenses.

Key Findings

The U.S. vital workforce will need to be kept alive and healthy for the duration of a biological threat scenario

  • Large-scale biological threats could cause much of the U.S. workforce to be simultaneously incapacitated or unwilling to work.
  • In many areas of the United States, there are simply not enough natural resources for the population to live off the land forever without industrialized food and water distribution, and some threat scenarios preclude this possibility.
  • Vital workers (VWs) are necessary to operate and maintain National Critical Functions, such as food processing, transportation, power utilities, and telecommunications functions.
  • For the purposes of these scenarios, the authors’ goal is to prevent more than 50 percent of VWs from becoming incapacitated by a biological threat.

In Scenario A, a fast-moving airborne respiratory pathogen is transmitted from human to human

  • Elastomeric half-mask respirators (EHMRs) with filtered exhalation, portable air cleaning tools, and other air decontamination tools may be useful to protect VWs and the general population.

In Scenario B, an airborne respiratory pathogen has extensive presymptomatic spread, infecting much of the population before it is aware

  • Short-read metagenomic sequencing of wastewater samples and long-read metagenomic sequencing of clinical nasal swabs may be able to detect the pathogen before it begins to spread.

In Scenario C, an airborne respiratory pathogen replicates and persists in the environment

  • Shelters positively pressurized with filtered air (safe zones) may help protect vital workers while indoors, and fully encapsulating suits may help protect those who must interact with the environment.

Recommendations

  • Stockpile (1) enough EHMRs with filtered exhalation to protect the vital workforce and (2) air decontamination tools to protect all vital workplaces with 2.5 equivalent air changes per hour.
  • Sequence 145 billion short reads daily from wastewater at ten major international airports and 16 million long reads daily from 10,000 nasal swab volunteers (all numbers are approximate).
  • Prototype and test safe zone designs and answer basic questions on collective protection and personal protective equipment performance.

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Patel, Aman J., Thomas Milton, Andrew Graham, Samuel Reynolds, Ulrik Horn, John P. Tarangelo, Saskia Popescu, and Greg McKelvey, Jr., Physical Approaches to Civilian Biodefense: Identifying Potential Preparedness Measures for Challenging Biological Threats. Santa Monica, CA: RAND Corporation, 2025. https://www.rand.org/pubs/research_reports/RRA4036-1.html.
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