The worst, possibly existential, threat is the stealthy, invisible one that multiplies exponentially—in the accurate sense of the term: 400 cases today, 800 tomorrow, then 1600, 3200, 6400, 128000, 256000, 512000, and 1.024 million after only eight doubling times. Biological threats proliferate—until they run out of susceptible victims.

In 1918, the great influenza pandemic killed as many people in 11 months as the medieval Black Death did in 4 years. Ultimately, at least 50 million may have perished. Young healthy people, especially young soldiers headed off to the front in World War I, succumbed quickly. To avoid interfering with the war effort, the U.S. government denied and covered up the threat, preventing the implementation of public health measures.

Since then, the world has gotten smaller. A virus that jumps the species barrier from animals to humans in a meat market in China can cross the Pacific in hours. And despite the expenditure of $80 billion on a National Biologic Defense, the U.S. is arguably no better prepared than it was in 1918, state Steven Hatfill, M.D., and coauthors in their new book Three Seconds until Midnight.

As in1918, we lack a vaccine or wonder drugs, but must rely on non-pharmaceutical interventions (NPI), and on public health authorities to track and try to contain the spread of infection.

Accurate information is critical. Can we trust governmental authorities to tell the truth? Travel restrictions, quarantine, closing businesses, and cancelling public events have a huge economic and potential political cost.

There can also be incentives to exaggerate the threat, in order to sell poorly tested vaccines or drugs. The 1976 swine flu epidemic was almost a non-event; more people were probably injured or even died from adverse effects of the heavily promoted vaccine.