Pandemic flu is a global outbreak of the influenza virus, with the culprit classically being influenza A. In order to be considered a pandemic flu, the virus must be spread easily from person to person, and be found in numerous regions of the world. This type of flu can also be highly virulent, and the human population typically lacks immunity to the virus. Historically, pandemic flu has claimed a disproportionate number of healthy young patients, in contrast with other strains of the flu, which tend to target the young, the elderly, and the immunocompromised.
Swine and avian flus are usually linked with pandemic flu. Pigs and birds appear to act as reservoirs for the flu, with periodic isolated outbreaks of avian and swine flu occurring all over the world. In most cases, people can only get the virus through direct contact with pigs or birds, but when the virus mutates so that it can be spread from person to person, it can develop into a pandemic flu, as influenza is easy to spread and hard to control when no vaccination or natural immunity is present.
The most infamous flu pandemic in history was the 1918 flu, also known as the Spanish Flu, which killed an estimated 40 million people worldwide. Two other pandemic flus emerged in the 20th century: the 1957 Asian Flu and the 1968 Hong Kong Flu. The nomenclature for pandemic flu outbreaks usually references the nation in which the flu was first identified, although some people prefer to reference the flu by its subtype, such as H1N1 flu. Subtypes are determined by looking for hemagglutinin and neuraminidase, two proteins on the surface of the virus.
The risk of pandemic flu is a major public health concern. The emergence of such flus can be difficult to predict, and it is challenging to make a vaccine for new strains of flu. Typically, pandemic flu is characterized by isolated mild outbreaks in the spring, which turn into a full blown pandemic in the fall as the flu virus spreads across the world. In the age of air travel and rapid communication between countries, pandemic flu is especially dangerous because patients can spread it before they even realize that they are sick.
Agencies such as the World Health Organization (WHO) monitor flu, looking for cases which appear to be suspicious, and maintaining a pandemic alert level to let the global health community know the probability of a flu pandemic. A number of governments have extensive systems in place which are designed to deal rapidly and effectively with pandemic flu, ranging from emergency plans in major cities which are intended to prevent the spread of flu to teams of epidemiologists which can be rapidly dispatched in the event that suspicious flu cases emerge.
