A scientist examines the bacteria responsible for tuberculosis at a laboratory in Marseille, France. (ANNE-CHRISTINE POUJOULAT/AFP/Getty Images)

Tom Inglesby, an infectious-disease physician, is director of the Johns Hopkins Center for Health Security. Eric Toner, an emergency physician, is a senior scholar at the center and led the Clade X pandemic exercise project.

A few months ago, a disease caused by an engineered biological weapon played the antagonist in a fictional outbreak scenario that ended with more than 100 million dead and the global economy crippled.

It was a frightening story with a real message for U.S. leaders responsible for ensuring the country's pandemic preparedness.

Nature continues to create serious biological threats, with the possibility of a deadly new pandemic influenza perhaps the most worrying. Far less recognized, but potentially even more alarming: The biotechnology revolution now underway is substantially lowering the bar for the creation of biological weapons that themselves could cause pandemics.

Policymakers need to pay much closer attention to the threats that could be posed by biologically engineered pathogens. There are still no licensed vaccines for most of the deadly viral pathogens that have occurred naturally in the past 40 years. That includes HIV, West Nile, severe acute respiratory syndrome (SARS) and Middle East respiratory syndrome (MERS). A pathogen that combined the lethality of any of these diseases with the ability to spread like influenza could cause extraordinary illness and mortality.

We and our colleagues at the Johns Hopkins Center for Health Security brought this threat to life in May with a tabletop exercise simulating the spread of a severe new pandemic involving a virus we called Clade X. Participants in the exercise included former Senate majority leader Thomas A. Daschle (D-S.D.) playing that role as American leadership formulated its response to the threat. Former deputy attorney general Jamie Gorelick served as attorney general in the simulation, which included mock newscasts and emergency National Security Council meetings.

The Clade X virus's origin as a bioengineered terrorist weapon and its pandemic trajectory shed light on feasible real-world threats and serious policy challenges. The exercise made clear that the only way to stave off a catastrophic outcome would have been a global public-health system capable of rapidly detecting a nascent outbreak and responding vigorously before it could become a pandemic. Such preparedness doesn't exist today.

Government and industry must be able to develop new medical countermeasures — and to manufacture and dispense millions of doses — within months rather than years, as current capabilities would require. The United States should place extraordinary national focus on establishing new approaches to quickly produce drugs, vaccines and rapid diagnostics for novel pathogens.

Sustained political commitment to pandemic preparedness is in some ways just as vital as the work to create medical countermeasures. The United States recognized the need by launching the Global Health Security Agenda in 2014, a five-year, $1 billion initiative. The aim was to establish an international effort to strengthen countries' ability to prevent, detect and respond to outbreaks. The initiative has been embraced by more than 60 countries so far, along with the World Health Organization and other organizations. The GHSA's successes so far include better tracking of multi-drug-resistant bacteria in Vietnam and faster responses to disease outbreaks in Uganda. But the GHSA's funding will run out next year, and although the Trump administration has expressed support for the initiative, future U.S. financial support is uncertain.

Investing in the GHSA directly benefits the health security of the United States because viruses don't respect borders. In the Clade X scenario, the virus first appeared in Venezuela and Germany before going global, eventually arriving in the United States. After 20 weeks, 15 million Americans were dead. The best way to prevent a local epidemic from becoming a pandemic is a robust, rapid, international public health and medical response that detects a disease early and stamps it out at its source.

But America must also fortify its national medical response capacity. We have some of the world's best hospitals, but the surge capacity in U.S. medical centers is severely limited, especially for highly infectious diseases. The vulnerability was graphically exposed when hospitals in the United States struggled to handle even a few Ebola patients five years ago. The nation barely passed that small test; we are still unprepared for a bigger challenge from natural viruses, much less bioengineered weapons.

Could a natural or man-made pandemic happen today? Yes. New lethal viruses are emerging from nature, and dizzying developments in biotechnology mean that biological weapons no longer are the sole province of a few state-sponsored programs — a manufactured pandemic could be unleashed by a rogue regime or by terrorists utilizing one of the thousands of laboratories around the world capable of making a dangerous pathogen. If the worst-case scenario unfolds, strong pandemic preparedness planning would save millions of lives. But progress is possible only with effective leadership.