A pandemic is a global infectious outbreak of a known or new emerging disease. A flu pandemic can occur when a new influenza A virus, like H1N1, emerges for which humans have little or no immunity and that is easily passed from person to person. The viruses can cause serious illness or death. Such an event may overwhelm hospitals and health centers around the world. A pandemic could also result in the closings of schools and businesses and other life disruptions.


The exact symptoms of pandemic flu are unknown. In previous pandemics, young healthy people carried a higher risk for serious complications.


A vaccine would probably be unavailable in the early stages of a pandemic. A pandemic would be triggered by three conditions, according to the Centers for Disease Control and Prevention:

  • A new flu virus subtype must emerge for which humans have little or no immunity;
  • The virus must infect humans and cause illness; and
  • The virus must spread easily and continuously among humans.


In the 20th century, three flu pandemics occurred – in 1918-19, 1957-58 and 1968-69. It is estimated that the Spanish Flu pandemic of 1918-1919 killed more than 20 million people worldwide. For further information visit