What is a pandemic
And to what extent should we worry about the current flu outbreak?

This article considers what is a pandemic - and to what extent we should worry about the current 2009 Type A H1N1 swine flu outbreak.

The dictionary pandemic definition is merely that it is something (for example, a disease) prevalent throughout an entire country, continent, or the whole world. It is a pretty wide definition.

The World Health Organisation (WHO), however, spells out more stringent conditions for it to decide what is a pandemic. According to the WHO pandemic definition, three conditions must be met before a disease such as the flu will be declared a pandemic:

• There must be a disease new to a population - or at least a disease that had not surfaced for a long time.
  
  
• This disease must be caused by disease-causing agents that infect humans, causing serious illness.
  
  
• The agents must spread easily and sustainably among humans.

These three conditions have already more or less been met. The current outbreak of flu is due to a new strain of virus. Even though it belongs to the same classification - Type A H1N1 - as existing strains, it is a new strain of virus and not a mutation of an existing strain.

The new virus does infect humans and the flu it causes can arguably be said to be "serious" - even though the death rate from the current type of flu is not as high as some previous types. What remains unclear is whether it will later mutate into a more lethal form of virus.

Finally, the new flu does spread easily, although how long it sustains remains to be seen, So in all likelihood, we can expect the WHO to declare the current flu outbreak as a full-blown pandemic anytime soon.

Pandemics vs epidemics: In considering what is a pandemic flu, we need to also understand the difference between a pandemic and an epidemic. Epidemic flus are also widespread, but they are caused by subtypes of existing flu viruses that ar already circulating. Pandemic flu outbreaks are caused by new subtypes, or by subtypes that had not surfaced for a long time.

Previous flu outbreaks give a better idea of what is a pandemic. In termperate countries, there is an annual "flu season" during the winter, when large numbers of people get the flu. These are epidemics, not pandemics. In the last 100 years, only three flu outbreaks fulfilled the conditions as to "what is a pandemic":

• 1918 Spanish flu, which was linked to a Type A H1N1 virus, the same type that is now linked to the Mexican swine flu.
• 1957 Asian flu, linked to a Type A H2N2 influenza virus
• 1968 Hong Kong flu, linked to a Type A H3N2 influenza virus.

Pandemic alert level

Besides a general pandemic definition, the WHO has developed a global influenza preparedness plan. This plan has six stages to define even more clearly what is a pandemic. Stage 6 is the most serious and, early in the current H1N1 swine flu outbreak, the WHO already decleared that it had reached Stage 5.

The different phases, or pandemic alert levels are as follows:

• Phase 1: No new influenza virus subtypes have been detected in humans. However, an influenza virus subtype that has caused human infection may be present in animals. In such a situation, the risk of human infection or disease is considered low.
  
  
• Phase 2: No new influenza virus subtypes have been detected in humans. However, a subtype of flu virus is believed to pose a substantial risk of human disease.

These two phases are considered the "pre-pandemic" period. The distincion between phases 1 and 2 is based on the risk of human infection. The next three are "pandemic alert" phases:

• Phase 3: The new virus subtype infects humans, but human-to-human spread either does not occur or is limited to close contact.
  
  
• Phase 4: Limited human-to-human transmission but the spread of the flu is highly localised, suggesting that the virus is not well adapted to humans.
  
  
• Phase 5: Larger cluster but human-to-human spread still localized, suggesting that the virus is becoming increasingly better adapted to humans but may not yet be fully transmissible (substantial pandemic risk).

Finally, this really is what is a pandemic:

• Phase 6: Increased and sustained transmission in the general population.

Is the 2009 H1N1 flu outbreak a pandemic?

Yes and no. And even the scientific experts cannot agree on this.

As of end-May 2009, about one month after the current flu virus first surfaced, the H1N1 swine flu virus has already affected more than 10,000 people in over 40 countries. Based on the standard definition of what is a pandemic, the current outbreak would already qualify as a pandemic.

But even though the infection has been widespread, the current flu outbreak has not been severe - as only a small number of people died from the disease. This is in contrast to earlier flu pandemics - the 1918 Spanish flu, 1857 Asian flu and the 1968 Hong Kong flu - where the mortality rate was high.

The outbreak of H5N1 avian flu that began around five years ago had a very high mortality rate of about 60 percent, And many scientists feared that avian flu might trigger the next pandemic. However, that did not spread widely enough to be called a pandemic.

Some scientists - and politicians - are now arguing that "pandemic" is too serious a term to describe the current H1N1 flu outbreak. The problem is, the existing WHO definition of what is a pandemic does not take into account severity. It only considers how widespread the disease is, not how many people it kills. And there have been calls for the WHO to change its definition of what is a pandemic.

The counter argument is that "we should call a fire a fire" and not define a fire according to how many people it kills. There are also concerns that the WHO will lose its credibility if it changes its pandemic definition, especially if it does so under political pressure. After all, scientists feel that they - and not politicians - should be the ones who decide what is a pandemic.

Meanwhile, the final severity of the current flu outbreak - whether or not it is called a pandemic - remains unknown. In previous flu pandemics, there had been two or more waves of infection and subsequent waves often proved more deadly than the original one.

To better understand what is a pandemic, read here about the 1918 Spanish flu.