What’s a pandemic?

An epidemic occurs when a greater-than-normal number of new cases of a certain disease pop up in a given area. A pandemic is an epidemic in populations across a large region.

(The "pandemic" label refers to the spread of a disease, not its severity.)

The World Health Organization (WHO) declares a pandemic when:

Verified human-to-human transmission of an animal or human-animal reassortant virus causes community-level outbreaks in at least two countries in one WHO region, and at least one country in a different WHO region.
As of 5/4/09, the world stood at pandemic alert level 5.

Historically, influenza pandemics occur every 30 – 40 years. The last one was in 1968, which leads some to say we're due for another outbreak.

Consequences of a pandemic

The most severe influenza pandemic of the 20th century occurred in 1918 – 1919 and caused 40 – 50 million deaths worldwide. Determined not to repeat the past, scientists have learned a lot about what happened in 1918.

Current epidemiological models project that a pandemic today could cause 2 – 7.4 million deaths around the world. (The current H1N1 outbreak is not currently expected to cause this level of illness or death.) Were an outbreak of that scale to happen, we could expect:

  • The virus to spread very quickly due to the high level of global traffic
  • A several-month wait for a vaccine to become available
  • A shortage of vaccines, antiviral drugs, and antibiotics
  • Overwhelmed medical facilities
  • Widespread illness that could cause shortages of people to perform essential community services.

With consequences like that on the line, WHO maintains more than 120 National Influenza Centers in 90 countries to monitor flu activity and isolate viruses in every region of the world. A rapid response is our best defense against the flu.