Pandemic influenza

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Flu viruses are constantly changing to produce new strains. Flu pandemics occur when a virus develops that is totally different to any previous strains.

Very few people will be immune to new strains as they will not have been exposed to it before. These conditions make it very easy for the virus to spread, affecting a huge number of people.

How is seasonal flu different to pandemic flu?


Seasonal Flu

Pandemic flu

Occurs every winter.

Occurs every few decades, at any time of year.

People affected experience an unpleasant but not life-threatening infection.

Infection is more serious, showing more severe symptoms.

People most at risk include: the very young, the very old and those with other serious illnesses.

Serious illness can occur in anyone of any age.

People most at risk can have an annual vaccination.

Vaccines cannot be developed until a pandemic strain emerges. Once a vaccine is produced, as many people as possible will be vaccinated.

Anti-viral drugs are also used to treat people most at risk.

Large amounts of anti-viral drugs are being stored ready to be used as required.


Large amounts of anti-viral drugs are being stored ready to be used as required.

Influenza pandemics have been well documented throughout history. They usually occur between 10 and 50 year intervals and cause many deaths in the young, elderly and those suffering with serious medical conditions.

Greek reports from as early as 412 Before Common Era (BCE) have shown possible influenza outbreaks, but these records are not very accurate.
History records suggest that there have been thirteen possible pandemics since 1580.
One of the worst recorded pandemics was ‘Spanish flu' (1918-1920) that infected 50% of the worlds population and was responsible for 20–40 million deaths worldwide. It has been suggested that the pandemic strain originally came from China or North America and was transmitted to Europe via a ship traveling to France in April 1918.

From France, the infection spread to soldiers that fought during World War I and continued to spread throughout Europe. During the next two years, the strain changed its characteristics (mutation) and became even more infectious with a 10-fold increase in death rates.

Future pandemics are predicted to start in China where over one quarter of the world’s population live close to poultry and pigs; well known for their spread of influenza. Pandemic patterns suggest that the next pandemic will be before 2017, but with increased scientific knowledge and immunisation, the impacts of this pandemic should be much less than previous pandemics.

Pandemics from the last century
Pandemic name Year Deaths worldwide Most affected group

Spanish flu

  • 1918-1919
  • 20-40 million

Healthy young adults (20-50 years)

  • Asian flu
  • 1957-1958
  • 1 million
  • Very young and very old

Hong Kong flu 1968-1969

  • 1-4 million
  • Very old and those with serious medical conditions


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