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Pandemic influenza information and situations can change quickly.

For the most up-to-date information on pandemic Influenza please visit the Flu.gov website.

Flu Pandemics

A pandemic is a global disease outbreak. An influenza pandemic occurs when a new influenza A virus emerges for which there is little or no immunity in the human population, begins to cause serious illness and then spreads easily person-to-person worldwide. A pandemic is determined by the spread of disease, not its ability to cause death.

Historically, the 20th century saw 3 pandemics of influenza, and the 21st has experienced 1 flu pandemic.

New Flu Viruses

There are three types of flu viruses. Type A viruses are found in many kinds of animals, including ducks, chickens, pigs, and whales, and also humans. The type B virus widely circulates in humans. Type C has been found in humans, pigs, and dogs and causes mild respiratory infections, but does not spark epidemics.

The influenza virus is one of the most changeable of viruses. Changes may be small and continuous or large and abrupt

Small, continuous changes happen in type A and type B influenza as the virus makes copies of itself. The process is called antigenic drift. The drifting is frequent enough to make the new strain of virus often unrecognizable to the human immune system. For this reason, a new flu vaccine must be produced each year to combat that year’s prevalent strains.

Type-A influenza also undergoes infrequent and sudden changes, called antigenic shift. Antigenic shift occurs when two different flu strains infect the same cell and exchange genetic material. The novel assortment of HA or NA proteins in a shifted virus creates a new influenza A subtype. Because people have little or no immunity to such a new subtype, their appearance tends to coincide with a very severe flu epidemic or pandemic.

Seasonal Flu vs. Pandemic Flu

Characteristics and Challenges of a Flu Pandemic

1. Rapid Worldwide Spread
  • When a pandemic influenza virus emerges, its global spread is considered inevitable.
  • Preparedness activities should assume that the entire world population would be susceptible.
  • Countries might, through measures such as border closures and travel restrictions, delay arrival of the virus, but cannot stop it.
2. Health Care Systems Overloaded
  • Most people have little or no immunity to a pandemic virus. Infection and illness rates soar. A substantial percentage of the world’s population will require some form of medical care.
  • Nations unlikely to have the staff, facilities, equipment and hospital beds needed to cope with large numbers of people who suddenly fall ill.
  • Death rates are high, largely determined by four factors: the number of people who become infected, the virulence of the virus, the underlying characteristics and vulnerability of affected populations and the effectiveness of preventive measures.
  • Past pandemics have spread globally in two and sometimes three waves.
3. Medical Supplies Inadequate
  • The need for vaccine is likely to outstrip supply.
  • The need for antiviral drugs is also likely to be inadequate early in a pandemic.
  • A pandemic can create a shortage of hospital beds, ventilators and other supplies. Surge capacity at non-traditional sites such as schools may be created to cope with demand
  • Difficult decisions will need to be made regarding who gets antiviral drugs and vaccines.
4. Economic and Social Disruption
  • Travel bans, closings of schools and businesses and cancellations of events could have major impact on communities and citizens.
  • Care for sick family members and fear of exposure can result in significant worker absenteeism.
Communications and Information are Critical Components of Pandemic Response

Education and outreach are critical to preparing for a pandemic. Understanding what a pandemic is, what needs to be done at all levels to prepare for pandemic influenza, and what could happen during a pandemic helps us make informed decisions both as individuals and as a nation. Should a pandemic occur the public must be able to depend on its government to provide scientifically sound public health information quickly, openly and dependably.