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What is swine flu (influenza A H1N1) ?

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Flu is an illness caused by an infection of the influenza virus. The flu virus constantly changes and there are many different strains of flu. Find out the differences between swine flu, pandemic flu, and ordinary flu.

What is it and how serious is it?

A new strain of Influenza A (H1N1), also known as swine flu, was confirmed in the UK in April and has spread to more than 100 countries around the world.

Although symptoms have generally proved mild, a small number of patients will develop more serious illness.  Many of these people have other underlying health conditions, such as heart or lung disease, that put them at increased risk.


Flu symptoms can include:

  • fever
  • cough
  • headache
  • weakness and fatigue
  • aching muscles and joints
  • sore throat
  • runny nose

As with any sort of influenza, how bad and how long the symptoms last will depend on treatment and the patient’s individual circumstances.

Most cases reported in the UK have been relatively mild, with those affected starting to recover within a week.

National Pandemic Flu Service

National Pandemic Flu Service

Who is at risk?

Some groups of people are more at risk of serious illness if they catch swine flu. It is vital that people in these higher risk groups get anti-viral drugs and start taking them as soon as possible – within 48 hours of the onset of symptoms.

Health authorities are still learning about the swine flu virus, but the following people are known to be at higher risk:

  • pregnant women
  • people aged 65 years and older
  • young children under five years old

People suffering from the following illnesses are also at increased risk:

  • chronic lung disease
  • chronic heart disease
  • chronic kidney disease
  • chronic liver disease
  • chronic neurological disease
  • Immunosuppression (whether caused by disease or treatment)
  • Diabetes mellitus
  • patients who have had drug treatment for asthma within the past three years

What is an epidemic and a pandemic?

An epidemic is a sudden outbreak of disease that spreads through a single population or region in a short amount of time.

A pandemic occurs when there is a rapidly-spreading epidemic of a disease that affects most countries and regions of the world.

Swine flu is now a pandemic. Pandemic flu occurs when an influenza virus emerges that is so different from previously circulating strains that few, if any, people have any immunity to it. This allows it to spread widely and rapidly, causing serious illness.

Ordinary flu and pandemic flu – the differences

Ordinary flu:

  • occurs every year during the winter
  • affects 10 to 15 per cent of the UK popuation
  • most people recover within 1 or 2 weeks without medical treatment
  • can be identified in advance and a vaccine can be made (this immunisation is known as the flu jab and helps protect people from ordinary flu)

Pandemic flu:

  • occurs during any season
  • affects more people than ordinary flu (up to half the population)
  • is a more serious infection
  • people of all ages may be at risk of infection
  • a vaccine cannot be made because the virus strain has not been identifed
  • antiviral medicine is stockpiled to treat people

How the flu virus spreads

For information on how swine flu is spread as well as how to prevent it and how it will be treated visit the ‘Swine flu – prevention and treatment’ page by following the link here.