Regional Homeland Security Coordinating Committee

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Pandemic Influenza

Seasonal flu is a contagious respiratory disease that is caused by influenza viruses. It occurs every year, typically in the fall and winter. Seasonal flu can cause serious illness and even death, and it poses a risk for people with weak immune systems. However, seasonal flu is usually not severe in most people, because they are already partly protected by having had a similar flu virus before. Annual flu shots also play a key role in protecting people from seasonal flu.

Pandemic flu is different and can be much worse. It can cause a worldwide outbreak of a new form of flu virus, which spreads easily from person to person because they have no immunity. Pandemic flu occurs when a flu virus goes through changes (called “mutations”) that create a new virus the body has never encountered. The infected person has no immunity to the new virus and is not prepared to fight it.
Because the new pandemic flu virus would be able to travel easily from person to person, it could spread quickly over long distances to millions of people worldwide. The result would be a flu pandemic.

During the 20th century, three serious influenza pandemics — the Spanish Flu in 1918, the Asian Flu in 1957, and the Hong Kong Flu in 1968 — killed millions of people. Because flu pandemics tend to occur in cycles, and because there has not been a major flu pandemic in many years, experts believe that we are due for one.

Where does pandemic flu come from?

Influenza viruses are constantly changing and producing new strains. Pandemics occur when a strain is so different from previous strains that few people, if any, are immune to it. This allows the new strain to spread widely and rapidly, affecting many hundreds of thousands of people worldwide.

How likely is it that pandemic flu will spread to the U.S.?

Health agencies are always on the lookout for the first signs of a flu pandemic, and will work to try to contain it. But once a flu pandemic affects other countries, it will most certainly reach the United States.

Who will be affected by pandemic flu?

Few people will have a natural immunity to pandemic flu, so most of the population is at risk. It will likely impact people of all ages, backgrounds and locations.

Is there a vaccine for pandemic flu?

A new vaccine must be developed for each new influenza virus. Because viruses change over time, it is difficult to produce a vaccine before the pandemic emerges in humans. Vaccine production is a complicated and lengthy process that can take several months.

How long will a pandemic last?

Predictions are difficult, but a flu pandemics may come in two or more waves several months apart, and each wave might last six to eight weeks in a particular location. In the 1957 pandemic, the second wave began three months after the first wave, but in 1968 the second wave began 12 months after the first.

What makes a pandemic different from other disasters?

Unlike other disasters, a flu pandemic is an infectious disease that does not damage homes, utilities, buildings and other structures. However, if the people who keep utilities and businesses running are unable to report to work, daily life will be disrupted.

For more information about what you can do to prepare for pandemic flu, contact your local public health department.