At the height of the swine flu pandemic this spring, when the US Centers for Disease Control and Prevention was recommending that schools with cases of H1N1 be closed for 14 days and Mexico was still on lockdown, the epidemiology community already suspected the world wasn’t ending. Why? The numbers came in: case fatality rate (how many infected people are dying) and replication rate (how many others an infected person will transmit the illness to — “R-zero,” in disease-speak). H1N1 had an RØ of about 1.3, high enough to spread the virus but low enough that a strong isolation program could break its back. Its case fatality rate was a wussy 1.9 percent in Mexico and 0.1 percent worldwide. By comparison, the 1918 Spanish flu had an RØ of 2.7 and a case fatality rate of up to 5 percent, making it far more deadly. A real apocalypse, like the killer flu in The Stand — Stephen King’s opus of epidemiologic eschatology — would be off the chart, with an RØ of 5 to 6 and a case fatality rate of 99 percent. So, don’t panic … unless H1N1 surges this fall. Where did we leave that hand sanitizer, again?

April 26

The first deaths from H1N1 are reported. US schools start closing. April 27

Everyone’s talking about swine flu. Stephen Colbert uses hand sanitizer as mouthwash on the air. April 28

Cuba becomes the first nation to ban travel to and from Mexico; Argentina and others follow suit. Mexico City shuts down. April 29

WHO raises the pandemic level alert to 5, “a strong signal that a pandemic is imminent.” April 30

Vice President Biden worries on the Today show: “When one person sneezes, it goes all the way through the aircraft.” May 5

The CDC reverses its earlier advice and recommends against the closing of K-12 schools in the US. May 6

Mexico City allows restaurants, cinemas, gyms, and churches to reopen. May 10

The CDC reports the third US swine flu fatality, in a patient who had multiple complicating illnesses. May 14

The Jonas Brothers delay concerts in Mexico due to fears of swine flu. May 18

Britain, China, Japan, and other nations urge WHO not to declare a pandemic. May 19

A CDC report suggests that obesity is one of the risk factors for H1N1 complications.

Why It Was Scary

Instead of opportunistically killing only children and the elderly, the 1918 Spanish flu killed many young adults. As of May 27, H1N1 was following the same pattern in Mexico. That’s a sign of a disease to fear.

Death and Illness

Showing illnesses and deaths on a linear graph makes clear the runaway exponential curve of Captain Trips and the simulated H1N1, and the more limited growth of real-life swine flu. Viruses spread exponentially as long as there is something to grow on (i.e. non-immune carriers) and a way to spread (i.e., no quarantine).

Spatial Distribution of Infected

This graphic is based on simulation performed with GLEaM (Global Epidemic and Mobility modeler). The simulation demonstrates the spread of this iteration of swine flu if it had the same characteristics as the 1918 version in terms of RØ and mortality. (Compare it with the real-life H1N1 map from GLEaM.) Ubiquitous air travel spread the simulated disease rapidly, leaving few places to hide — the flu will get to wherever people are.

World-Wide Projections

This report demonstrates the spread of this iteration of swine flu worldwide if it had the same characteristics as the 1918 version in terms of RØ and mortality, but included air travel among the infected. (Compare it with the real-life H1N1 map from GLEaM.)

Illustrations: Peter and Maria Hoey.

Timeline: April 26 and 28, May 7, 10, 18, and 20: Corbis; April 29 and May 6: AP; May 14: Disney Enterprises, Inc.

Sources: Alex Vespignani and Bruno Goncalves, School of Informatics and Department of Physics at Indiana University; Mexico Secretary of Health; the CDC; WHO; The Stand by Stephen King