Pandemic simulations first started gaining popularity in the 2000s. Biosecurity and public-health specialists took their cue from war-game exercises used by the military, in an effort to stress-test health systems, see what could go wrong and scare policymakers into fixing the problems. In these round-table events, academics, business leaders and government officials made real-time decisions to deal with an expanding crisis, laid out in television-news-style reports.

Two early simulations involved biological attacks, in which other countries unleashed smallpox in the United States. Operation Dark Winter, in 2001, and Atlantic Storm, in 2005, were orchestrated by biosecurity think tanks in the United States and attended by influential leaders, such as the former head of the World Health Organization (WHO), Gro Harlem Brundtland, and Madeleine Albright, the secretary of state under former president Bill Clinton (see ‘Games without frontiers’).

During the course of Dark Winter and Atlantic Storm, participants found that power struggles between federal and state leaders bogged down a health response as the epidemic doubled and quadrupled. Hospitals were unable to handle the influx of people requiring care, and national vaccine stockpiles ran dry. Tom Inglesby, director of the Center for Health Security at Johns Hopkins University in Baltimore, Maryland, which helped to lead both of the exercises, says that along with the fresh memory of terrorist and anthrax attacks in 2001, these events encouraged the US Congress to act. Not long after the Dark Winter exercise, the US government committed to developing a national supply of smallpox vaccines. And in 2006, Congress passed the Pandemic and All Hazards Preparedness Act, to improve the nation’s public-health and medical response capabilities in the event of an emergency. This included funding for research on emerging infections.

Anxiety about pandemics was also rising internationally. Not long after the 2003 outbreak of severe acute respiratory syndrome (SARS) spread to more than two dozen countries, and killed 721 people in mainland China, Hong Kong and Taiwan, the 194 member states of the WHO agreed to bolster the world’s defences against health threats through a set of rules called the International Health Regulations. These included commitments by countries to invest in pandemic preparedness, and to report outbreaks to the WHO so that other nations could be alert. The regulations were put to the test in 2009, when an H1N1 influenza virus is estimated to have killed more than 100,000 people, and again in 2013, with the spread of Middle East respiratory syndrome (MERS). Then came the world’s largest outbreak of the Ebola virus, in 2014–16, which killed around 11,000 people — roughly half of those infected.

In response to the drumbeat of epidemics, the United Nations commissioned a panel to explore how the world could better prepare for future threats. The resulting 2016 report made several recommendations, including investment in vaccines, therapeutics and diagnostics for emerging infectious diseases — and a need for “all relevant responders” to take part in infectious-disease simulations (see go.nature.com/2pc4bst).