1.3 The differences between pandemic flu and 'ordinary' flu
There are important differences between 'ordinary' flu and pandemic flu (see Table 1.2 below). These differences explain why we regard pandemic flu as such a serious threat. Epidemics of 'ordinary' flu occur every year around the world. An epidemic is a widespread outbreak of disease in a single community, population or region. A pandemic, on the other hand, spreads around the world affecting many hundreds of thousands of people across many countries. The word pandemic comes from the Greek words pan, meaning 'all,' and demos, meaning 'people.' Other diseases of pandemic proportions include HIV/AIDS and tuberculosis.
1.3.1 Key characteristics of pandemic flu
There are a number of key characteristics which experts look for when deciding whether or not a particular flu virus is a potentially pandemic strain.
For an influenza virus to be capable of causing a pandemic, it must be able to:
- infect people (not just mammals and birds)
- cause illness in a high proportion of those infected
- spread easily from person to person
- spread widely because the virus is significantly different from previously circulating strains and most people will have little or no immunity to it.
All previous flu pandemics exhibited these characteristics.
Table 1.2 The differences between ordinary and pandemic flu
| | Ordinary flu | Pandemic flu |
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| | - Ordinary flu occurs every year during the winter months in the UK.
- It affects 10-15% of the UK population, causing around 12,000 deaths every year.
- Globally, epidemics of 'ordinary' flu are thought to kill between 500,000 to 1 million people every year.
- Most people recover from ordinary flu within one or two weeks without requiring medical treatment.
- Deaths are generally confined to 'at risk' groups including:
- elderly people over 65 years of age
- people with existing medical conditions such as lung diseases, diabetes, cancer, kidney or heart problems
- people whose immune systems are compromised due to HIV/AIDS or because they have a transplant, for example
- the very young. - The vaccine against ordinary flu is effective because the virus strain in circulation each winter can be fairly reliably predicted.
- Annual vaccination, when the correct virus strain is fairly reliably predicted, and antiviral drugs are available for those at risk of becoming seriously ill.
| - Pandemic flu occurs roughly every thirty years and can take place in any season.
- It affects many more people than 'ordinary' flu - a quarter or more of the population - and is associated with much higher rates of illness and death. For example, the worst flu pandemic last century - the 1918 'Spanish Flu', caused around 250,000 deaths in the UK alone and up to 40 million deaths worldwide.
- Pandemic flu, usually associated with a higher severity of illness and consequently a higher risk of death, represents a much more serious infection than ordinary flu.
- People of all age groups may be at risk of infection with pandemic flu, not just 'at risk' groups.
- A vaccine against pandemic flu will not be available at the start of a pandemic. This is because the virus strain will be completely new. It will be different from the viruses that circulated the previous winter, and not predictable in the same way.
- Antiviral drugs may be in limited supply, their use depending on evidence of their efficacy which will only emerge once the pandemic is under way. (Treatment available for pandemic flu is described in more detail in Chapter 3).
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